Facebook has grown as fast as any company in the Seattle area in recent years, but it has done so while keeping details close to the vest, for the most part. But the company today disclosed the size of its massive, sprawling footprint throughout the region: 2.7 million square feet and counting.

That footprint works out to nearly twice the size of Seattle’s tallest skyscraper, Columbia Center.

Facebook’s regional presence includes a number of projects still under construction and in early planning phases. Facebook confirmed plans for a mysterious project known as Building X for its Oculus virtual reality unit. That building will become a centerpiece for the rapidly expanding Oculus campus in Microsoft’s backyard of Redmond, Wash.

Also part of Facebook’s growing footprint is a 338,000-square-foot building in the new Spring District neighborhood that the company recently leased.

The Spring District is a 36-acre, 16-block mixed-used development built around a future light rail station that will be home to a new headquarters for outdoor retailer REI. It is also the site of the Global Innovation Exchange, the technology innovation graduate program created by the University of Washington, Tsinghua University and Microsoft.

The neighborhood is being built from scratch, so there is plenty of future room for Facebook to grow there if it wants to create a clustered, campus-like environment.

Facebook said late last year its Seattle-area headcount topped 3,000 people, but that number is sure to increase exponentially as the company fills in these new buildings. Using conventional office space ratios as an estimate, Facebook’s future capacity could be somewhere between 13,500 to 18,000 people. However, much of the Oculus campus is for lab and research space, requiring more space per employee, so the capacity is probably somewhere close to 10,000.

Facebook is among the most prominent examples of out-of-town companies, specifically those from the San Francisco Bay Area, parachuting into Seattle to take advantage of the region’s stellar tech talent. Facebook opened its first Seattle engineering office in 2010, employing just a couple people near Pike Place Market, and later moved to occupy multiple floors in the Metropolitan Park complex near Interstate 5.

Facebook’s Seattle growth really kicked into high gear in 2016 after the company built out an office with room for 2,000 people designed by noted architect Frank Gehry. In the next few years, the company opened a new building nearby in the South Lake Union neighborhood, aka Amazon’s backyard, and leased a 384,000-square-foot project developed by Paul Allen’s Vulcan a couple blocks away.

Much of Facebook’s most recent expansion in the region has come outside Seattle, part of a broader trend of tech companies establishing operations on both sides of Lake Washington. Another prime example this year was Amazon leasing the entire Expedia headquarters building, as the travel giant prepares to move its headquarters to the Seattle waterfront.

Facebook wouldn’t say how big the campus for Oculus/Facebook Reality Labs in Redmond has gotten, but it’s clear that it makes up a major part of the company’s footprint in the region. GeekWire research pegs the Oculus campus at somewhere between 1 million and 1.4 million square feet, should the Building X project come to fruition.

Reports of Building X, a two-building project totaling 650,000 square feet, per early planning documents, first popped up in October. The site of the project is along Willows Road, where the Oculus campus has sprouted, on two parcels it bought earlier this year for $20 million.

Oculus has been on a hiring spree to fill up all this space, and it lists 190 open positions in Redmond on its job board. Facebook lists a total of 415 job openings in Seattle and Redmond combined.

In recent months, Facebook has set its sites on Bellevue. It started by leasing space in a pair of downtown buildings totaling 85,000 square feet. The company set a big old “Like” flag down in Bellevue with the lease of the Spring District building, and it wouldn’t be surprising if Facebook took down more space there in the future.

Facebook’s growth puts it among the biggest office users in the area, however, it still pales in comparison to hometown tech giants Amazon and Microsoft. Microsoft’s sprawling Redmond headquarters totals 15 million square feet in 125 buildings on more than 540 acres and is in the midst of a big redevelopment project.

GeekWire research found in 2017 that Amazon’s footprint in the Seattle region was approaching 13.5 million square feet. That number is a moving target as the company may sublease some space in Seattle while scooping up more buildings in Bellevue.