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Three million people now use Slack every day

It's also adding a million users every five months, the company says.

Slack co-founder Stewart Butterfield
Asa Mathat

Office productivity app Slack gave the latest look at its user metrics ahead of an event today.

Here's a preview: It's growing crazy fast and that growth is speeding up. Slack now boasts three million daily active users, up from two million as recently as December. The number of paid seats — users whose companies are at the paid level of service — rose to 930,000, up from 800,000 when last disclosed. At its current clip, it's adding a million active users every five to six months.

Slack also says that as many as two million individual users are regularly connected to the service simultaneously, which shows that, so far, the product can scale up without failing. The more users who can sign on to the service without seeing a disruption, the more comfortable large companies will feel about using it.

About those large companies: Slack says it is now used at 77 percent of the Fortune 100. In most of those cases it starts out in use in a single department and then spreads. When those teams get bigger, they upgrade from the free version to the paid version.

All this comes on the heels of Slack's recent fund-raising efforts. Last month it confirmed that it had landed $200 million in a round led by Thrive Capital at a valuation of $3.8 billion. As Silicon Valley's darling of the moment, it will have to keep the user numbers roaring to justify the lofty financials.

Interview of Slack's Stewart Butterfield and other CEOs

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