How Did Slack Grow So Fast? From 200 Users to $27.7B

Slack had fewer than 200 real users before its preview release in August 2013.

On the first day of that release, more than 8,000 people asked for an invitation.

A year and a half later, Slack had 500,000 daily active users. By January 2019, it had more than 10 million. Salesforce agreed to buy the company in 2020 in a deal valued at about $27.7 billion.

Slack's growth is often described as pure product-led growth or word of mouth.

That is only part of the story.

Slack used press to create its first big wave of demand. Then it carefully turned interested individuals into active teams. A free plan removed the need for procurement. Integrations made Slack more useful throughout the day. Word of mouth brought in new teams. Later, enterprise sales helped Slack expand from individual departments to entire companies.

The basic growth loop looked like this:

press and word of mouth → one person tries Slack → coworkers join → conversations move into Slack → Slack becomes a habit → the team pays → Slack spreads to more teams

That loop took Slack from a tool built inside a failed game company to one of the fastest-growing business software products of its era.

Slack's growth in numbers

Date	Milestone
Early 2013	8 employees begin building Slack
Before Aug. 2013 preview	Fewer than 200 real users across fewer than 20 teams
Aug. 2013	8,000+ invitation requests on the first day
Feb. 2014	About 16,000 daily active users
Aug. 2014	About 140,000 daily active users
Feb. 2015	500,000 daily active users and 135,000 paid seats
Dec. 2015	2 million daily active users and 570,000 paid seats
Oct. 2016	4 million daily active users and 1.25 million paid seats
Jan. 2019	10 million+ daily active users and 88,000 paid customers
FY2019	$400.6 million in revenue
Dec. 2020	Salesforce announces plan to buy Slack for about $27.7 billion
Jul. 2021	Salesforce completes the acquisition

The important part is what happened between those milestones.

Slack started inside a failed video game

Slack was not the original product.

Stewart Butterfield and his team at Tiny Speck were building an online game called Glitch.

The team was spread across cities including Vancouver, San Francisco, and New York. They needed a better way to communicate.

They already used Internet Relay Chat, or IRC, but it had problems. Messages disappeared when people were offline. Search was poor. Mobile access was limited.

So the team began building its own tools.

They logged and indexed messages. They added file sharing. They connected other software to chat so things like deployments, support requests, purchases, and database warnings appeared in the same place.

Over time, email became less important.

The system was messy, but the idea was powerful: put the company's conversations and information in one searchable place.

Glitch itself failed.

Tiny Speck shut the game down in late 2012 and laid off most of its roughly 40 employees.

But the team did not want to go back to working without the communication system it had built.

That became the seed of Slack.

Eight people rebuilt the internal tool as a product

Eight remaining employees began working on Slack in January 2013.

They did not simply package up the software they had used while building Glitch.

Much of it had been held together with internal hacks. They took what they had learned and built a real product around it.

By March, the team was using Slack itself.

That created another problem.

Slack's developers were experienced software workers. They already understood ideas such as channels, commands, and IRC-style communication.

Most office workers did not.

The team needed to find out whether Slack worked for people outside Tiny Speck.

Slack got its first users by asking friends

In May 2013, Butterfield started asking friends at other companies to try Slack.

He later said they "begged and cajoled" people into using it.

About six to ten companies agreed.

Two of the better-known early users were rental software company Cozy and music service Rdio.

Slack did not test with hundreds of companies at once.

It started small and slowly added larger teams.

That turned out to be important.

Rdio first used Slack inside a small development group. It then spread across engineering and eventually to all 120 employees.

Slack suddenly looked very different.

Features that worked for a small group became confusing at a larger scale. The channel list, for example, became harder for new users to understand.

Slack added things such as channel descriptions and member counts.

Then the team repeated the process.

Test with a group.

Watch what breaks.

Fix it.

Invite a larger group.

This gave Slack months to improve the product before opening it to the public.

Slack was selling a change in behavior

Slack's biggest competitor was not another chat app.

It was the way people already worked.

Most companies were not searching Google for "team chat software."

They used email, meetings, text messages, Skype, IRC, and whatever else was already available.

Butterfield understood this early.

In a July 2013 internal memo called We Don't Sell Saddles Here, he argued that Slack should not sell itself as another messaging tool.

Slack was selling the result:

less email
easier access to company knowledge
fewer missed conversations
better search
faster communication
more visibility across a team

Butterfield called it "organizational transformation."

This mattered because switching an entire team to a new communication tool is hard.

One person might like Slack.

But Slack only became useful when that person persuaded coworkers to use it too.

The product therefore had to be easy enough that a Slack champion could introduce it without making coworkers regret the change.

Design reduced the cost of switching

In the summer of 2013, Slack hired design agency MetaLab for a six-week design project.

The work helped shape Slack's early colors, avatars, applications, and visual identity.

This was not just about making the product look nice.

Slack was asking people to change something they did dozens or hundreds of times each day.

Every confusing screen gave someone another reason to go back to email.

So Slack put unusual care into details that enterprise software often ignored.

The product was colorful.

The writing was playful.

Uploading files was easy.

Search was fast.

Notifications were understandable.

Slackbot helped new users understand how the product worked.

That made Slack feel less like traditional enterprise software and more like a consumer product people actually wanted to use.

Press created Slack's first big spike

Slack opened its Preview Release in August 2013.

The word "preview" was deliberate.

Butterfield did not want to call it a beta because people might assume the product was unreliable. That was a dangerous impression for software asking teams to move important conversations into it.

Slack's marketing goals were modest.

James Sherrett, who later became Slack's first marketing hire, wrote that the team hoped for:

coverage from half of the top technology blogs
25,000 website visits
1,000 signups
200 new teams

Before the release, Slack had fewer than 20 teams and fewer than 200 real users.

Slack used a PR agency to coordinate briefings with reporters. Butterfield could also draw on his reputation as a co-founder of Flickr.

Investors including Andreessen Horowitz and Accel helped introduce Slack to companies in their portfolios.

TechCrunch, AllThingsD, and other technology publications covered the launch.

The result was far bigger than expected.

More than 27,000 people visited Slack's simple website.

More than 8,000 requested an invitation on the first day.

Within roughly one to two weeks, the number had reached around 15,000 to 16,000.

This distinction matters:

Slack did not gain 8,000 active users on day one. It gained 8,000 invitation requests.

The PR campaign created curiosity.

Slack still had to turn those people into real teams.

Slack deliberately slowed down growth

A normal startup might try to let everyone in immediately.

Slack did the opposite.

It released invitations in batches.

James Sherrett personally worked through close to 1,000 early teams. The company read what users told them and compared that with what people actually did inside Slack.

When a batch of users produced the same support problem, Slack sometimes stopped sending invitations.

The team fixed the problem first.

Then it let more people in.

Sometimes the delay lasted a day.

Sometimes it lasted a week.

Support volume effectively acted as a release gate.

This allowed Slack to grow without letting a poor first experience destroy word of mouth.

Customer support became part of product development

Slack treated customer support as one of its main ways to learn.

Ali Rayl, one of Slack's original eight employees, helped build the company's customer support system.

Feedback from tickets and social media was tagged and sent into searchable Slack channels where the product team could see it.

Butterfield also spent time answering people on Twitter.

This was especially important for a team product.

Imagine convincing your coworkers to try a new communication tool.

Then it breaks.

You do not just blame the software. Your coworkers may blame you for making them switch.

Fast support helped protect the person who had introduced Slack to the company.

By early 2015, Slack said it was receiving roughly 8,000 Zendesk tickets and 10,000 tweets each month and responding to all of them.

The support team was not separate from growth.

It helped make adoption work.

Slack's early funnel had a huge amount of drop-off.

More than 90% of people who completed the form to create a Slack team never invited anyone or started seriously using the product.

By early 2015, roughly 220,000 teams had been created.

Only around 30,000 were active.

For many companies, that would look terrible.

Slack understood that the important metric was not how many workspaces people created.

It was whether a team actually moved its work into Slack.

The 2,000-message rule became Slack's activation metric

Slack found one particularly useful signal.

2,000 messages.

Butterfield said that once a team had exchanged 2,000 messages, Slack considered that team to have properly tried the product.

For a team of 10 people, reaching 2,000 messages might take roughly a week.

At the time Butterfield discussed the metric, 93% of teams that had passed 2,000 messages were still using Slack.

The number has often been simplified into:

Reach 2,000 messages and 93% of customers will stay.

That is stronger than the evidence supports.

Slack had found a correlation.

It did not publish a causal experiment showing that sending message number 2,000 caused a team to retain.

The real insight was simpler:

Slack needed to measure team activation, not individual signup.

A workspace with one curious user had little value.

A workspace where coworkers had already exchanged thousands of real messages was much more likely to have become part of daily work.

That gave Slack a clearer question for onboarding:

How do we help a team reach meaningful use?

The free plan removed the buying decision

Slack launched publicly on February 12, 2014.

At the time, it had around 16,000 daily active users across roughly 1,500 teams.

It also introduced paid plans.

But teams did not need to pay to get started.

The free version included:

the most recent 10,000 searchable messages
5 GB of storage
five integrations

The Standard plan cost $8 per user per month, or $6.67 with annual billing.

The Plus plan cost $15 per user per month.

This was critical to Slack's growth.

A few employees could try Slack without:

talking to procurement
requesting a company budget
booking a sales demo
convincing an executive
signing a long contract

They could simply create a workspace and invite coworkers.

That reversed the usual enterprise software sales process.

Traditional software often moved:

executive → IT department → employees

Slack could move:

employee → team → department → company

Slack made paying feel like the natural next step

Slack's free plan was generous enough to let a team experience the product.

But it also became more valuable the longer people used it.

A team might eventually have thousands of messages containing:

decisions
links
files
customer discussions
project history
company knowledge

On the free plan, only the latest part of that archive remained searchable.

Paying made more of the history available.

Larger companies also needed things such as better administration, security, compliance, and support.

Slack added another small detail that reduced the risk of upgrading: fair billing.

Customers paid for active seats. If someone stopped using Slack, the company could receive prorated credits rather than continuing to pay for an unused account.

This made companies less afraid to invite more people.

Word of mouth became Slack's main growth channel

The preview release depended heavily on PR.

What happened afterward was different.

People loved Slack and talked about it.

The company became famous for its "Wall of Love," which collected enthusiastic tweets from users.

By October 2014, Butterfield said growth had happened almost entirely through word of mouth.

Slack had only recently hired its first marketing employee.

The product had several reasons to spread naturally.

First, Slack was collaborative.

One person could not get much value from an empty workspace. They had to invite coworkers.

Second, people who liked Slack often introduced it to another team or brought it with them when they changed jobs.

Third, once one department used Slack heavily, employees elsewhere in the company could see it working.

Slack's distribution was therefore built into normal product usage.

It was not perfectly viral. Every new user still needed a reason to join.

But every successful team created more people who knew how Slack worked and could introduce it somewhere else.

Slack's integrations made the product more useful every day

Slack did not try to build every workplace tool itself.

Instead, it connected to them.

GitHub commits could appear in Slack.

Dropbox and Google Drive files could be shared there.

Support tickets could show up in channels.

Monitoring systems could send alerts.

Project tools could send updates.

This did two things.

First, it made Slack useful even when nobody was actively chatting.

Software itself produced useful messages.

Second, it made Slack a place where information from many different tools came together.

Slack became less like a chat app and more like the place where a team watched work happen.

In December 2015, Slack launched its App Directory with 150 approved apps and announced an $80 million developer fund.

At the time, Slack had reached:

2 million daily active users
570,000 paid seats

Developers had already created thousands of integrations.

By January 2019, Slack's directory contained more than 1,500 apps. Its S-1 said more than 500,000 developers were registered on the platform, while more than 450,000 third-party apps or custom integrations were used during a typical week.

The ecosystem made Slack more useful.

It also made Slack harder to replace.

Slack moved from teams to enterprises

Bottom-up adoption worked well for small teams.

It was not enough for the largest companies.

Big businesses needed:

security controls
centralized administration
compliance
legal agreements
identity management
uptime guarantees
company-wide policies

Slack gradually built these features and added a direct sales organization.

It launched Enterprise Grid in January 2017.

Companies including IBM, Capital One, and PayPal had tested it.

This gave Slack a second growth engine.

The product could still enter a company through employees.

Then Slack's sales team could help expand it across the organization.

In other words:

product-led growth landed the account; enterprise sales expanded it.

Slack's customer expansion became a major growth engine

By January 31, 2019, Slack had:

more than 10 million daily active users
more than 600,000 organizations with at least three users
88,000 paid customers
575 customers producing more than $100,000 in annual recurring revenue

Revenue reached $400.6 million in fiscal 2019, up 82% from the previous year.

Slack's net dollar retention was 143%.

That means the same group of customers, as a whole, was spending substantially more with Slack than it had the year before, even after accounting for customers that reduced spending or left.

Slack had built a powerful expansion model.

Get into one part of a company.

Get used every day.

Add more employees.

Add more departments.

Move the company onto a larger plan.

Microsoft changed Slack's growth story

Slack went public through a direct listing in June 2019.

Its shares opened at $38.50, well above the New York Stock Exchange's $26 reference price.

But Slack now faced a competitor with a distribution advantage it could not easily copy.

Microsoft had launched Teams in 2016 and later included it with Office 365.

Millions of businesses already paid Microsoft for workplace software.

Microsoft did not have to persuade each company to buy another standalone collaboration product. Teams could arrive as part of software the company already used.

By July 2019, Microsoft reported 13 million daily active Teams users, above Slack's previously reported 10 million.

The companies did not always measure usage in exactly the same way, but the direction was clear.

Slack had proven that workplace chat could become a huge category.

Microsoft could bundle that category into an existing suite.

The pandemic helped Slack, but helped Microsoft too

Remote work exploded in 2020.

Slack benefited.

During the quarter ending April 30, 2020, it added:

more than 90,000 net new free or paid organizations
12,000 net new paid customers

Paid users were active for more than 120 minutes per day on average at quarter-end.

Revenue grew 50% year over year to $201.7 million.

But Slack did not get a Zoom-like breakout from the pandemic.

Microsoft had Teams bundled with Office 365.

Companies facing economic uncertainty could often use a collaboration product they were already paying for instead of adding another vendor.

Slack finished the fiscal year ending January 31, 2021, with:

$902.6 million in revenue
156,000 paid customers
123% net dollar retention
more than 600,000 free organizations

By then, the company had become a large software business.

But competing alone against Microsoft was becoming harder.

Salesforce bought Slack for about $27.7 billion

On December 1, 2020, Salesforce announced an agreement to acquire Slack.

Slack shareholders would receive $26.79 in cash plus 0.0776 Salesforce shares for each Slack share.

Salesforce described the deal as having an enterprise value of approximately $27.7 billion.

The acquisition closed on July 21, 2021.

Salesforce later recorded roughly $27.1 billion as the acquisition-date fair value of the consideration.

Those two numbers measure the transaction at different points, so they should not be treated as contradictory.

Slack is now part of a much larger platform

After the acquisition, Salesforce gradually stopped reporting Slack as a fully separate business.

That makes its standalone growth harder to measure.

Salesforce disclosed $1.5 billion in Slack subscription and support revenue for fiscal 2023, but later grouped Slack with other products.

Slack remains an important part of Salesforce's strategy, particularly as Salesforce tries to make it the interface where employees work with AI agents.

And the product is still growing.

In Salesforce's August 2026 earnings report, the company said Slack produced its fastest quarterly growth in net new annual order value since the acquisition. Salesforce also said Slackbot users had grown more than 150% from the previous quarter.

The product is very different from the Slack that launched in 2013.

The original growth mechanism, however, is still easy to see.

Get into the daily flow of work.

Become useful to the whole team.

Then become difficult to remove.

Slack's growth strategy in 7 steps

Slack's growth can be reduced to seven main moves.

1. Test with small groups before scaling

Slack started with six to ten friendly companies and moved to progressively larger teams.

This showed the company where the product broke before millions of people could experience those problems.

2. Use press to create initial demand

Slack's first major spike did not come from a viral loop.

It came from a coordinated launch, Butterfield's network, investors, and technology press.

More than 8,000 people requested invitations on the first day.

Slack did not immediately admit everyone who wanted access.

It released users in batches and sometimes paused invitations while fixing repeated problems.

4. Measure team activation

Slack learned that creating a workspace did not mean much.

The useful signal was whether a team actually moved conversations into the product.

Its famous 2,000-message threshold helped identify teams that had genuinely tried Slack.

5. Remove the buying barrier with freemium

Small teams could start using Slack without sales calls or procurement.

That allowed adoption to begin from the bottom of an organization instead of the top.

6. Make the product spread through normal use

Slack needed coworkers to participate.

Every active team therefore introduced the product to more people.

Happy users also brought Slack to new teams and new employers.

7. Add enterprise sales after bottom-up adoption worked

Slack did not rely on product-led growth forever.

Once the product was already spreading through companies, enterprise features and salespeople helped turn departmental adoption into large contracts.

What people get wrong about Slack's growth

"Slack got 8,000 users on launch day"

Not exactly.

Slack received more than 8,000 requests for invitations on the first day of its August 2013 preview.

Before the preview, it had fewer than 200 real users.

The hard part came afterward: turning that interest into active teams.

"Slack grew entirely through word of mouth"

Word of mouth became extremely important.

But Slack's first major demand spike came from PR.

Its launch was carefully planned, reporters were briefed in advance, Butterfield's Flickr reputation helped, and investors introduced Slack to companies.

"Slack was completely viral"

Slack had a natural invitation loop because a communication product needs multiple people.

But that does not mean every user automatically produced another user.

Someone still had to convince coworkers to change how they communicated.

Slack's support, onboarding, design, and free plan made that change easier.

"2,000 messages caused 93% retention"

Slack found that 93% of teams that had passed 2,000 messages were still using the product at the time Butterfield discussed the metric.

That was a correlation.

Slack did not publish evidence showing that crossing message number 2,000 itself caused retention.

What startups can learn from Slack

Slack's biggest lesson is not "build a viral product."

It is that growth depends on understanding the real unit of adoption.

For Slack, the user was not enough.

The team had to change its behavior.

That changed almost everything about the company's growth strategy.

Slack tested with whole teams.

It measured team activation.

It built onboarding around coworkers.

It used free access to avoid procurement.

It made integrations valuable to entire organizations.

And later, it used enterprise sales to expand teams that had already adopted the product.

The press campaign explains how Slack went from fewer than 200 users to thousands of people waiting to try it.

It does not explain how Slack reached 10 million daily active users.

That came from converting attention into a habit.

Most startups won't get Slack's press. The word-of-mouth half is more reachable: show up where your users already talk. Okara's Reddit Agent finds those conversations and drafts replies, and the X Agent keeps your founder story in front of people who'll repeat it.

Frequently asked questions

How did Slack get its first users?

Slack first used the product internally. In May 2013, Stewart Butterfield persuaded roughly six to ten friendly companies, including Cozy and Rdio, to test it. Slack then added progressively larger teams and used their feedback to improve the product before its public preview.

How did Slack grow so quickly?

Slack combined a strong press launch with bottom-up product adoption. Teams could start for free, invite coworkers, connect the tools they already used, and upgrade later. Word of mouth brought Slack into new teams, while enterprise sales eventually expanded adoption across larger companies.

How many users did Slack have when it launched?

Before its August 2013 preview, Slack had fewer than 200 real users. More than 8,000 people requested invitations on the first day of the preview. When Slack launched publicly in February 2014, it had around 16,000 daily active users.

What was Slack's 2,000-message rule?

Slack found that teams that had exchanged 2,000 messages were much more likely to keep using the product. Stewart Butterfield said 93% of teams that crossed that level were still using Slack when measured. It was an activation signal, not proof that sending exactly 2,000 messages caused retention.

Did Slack use product-led growth?

Yes. Slack is one of the best-known examples of bottom-up product-led growth in B2B software. Teams could start using the free product without talking to sales. Slack later added enterprise sales to expand inside large organizations.

Did Slack grow without marketing?

No. Slack relied heavily on PR for its 2013 preview release. Its early marketing campaign generated more than 8,000 invitation requests on the first day. Word of mouth became a major growth channel after teams began using and recommending the product.

How much did Salesforce pay for Slack?

Salesforce announced the acquisition in December 2020 at an enterprise value of approximately $27.7 billion. The transaction closed in July 2021.