Office Space for Lease in Flatiron District

Flatiron is where the AI money is going. It’s not the only place, but it’s the busiest one. For two years now the fastest-growing software and AI companies in New York have been signing leases between Union Square and Madison Square Park, and this year that went from a trend to the main thing driving the market. Savills says Midtown South availability fell 470 basis points to 14.4% as tech and AI companies kept absorbing space, and a lot of that demand is landing right here in Flatiron and along Park Avenue South (Savills, Q3 2026).

But the headlines leave something out: Flatiron is really two markets. Up on Park Avenue South and around Madison Square Park, AI and fintech tenants are signing from $90 to $120/SF and buildings are hitting 100% leased. Three blocks west, on the Sixth Avenue side and the prewar side streets, there’s still real loft space at real prices for a growing company that doesn’t need to make a statement. Where you land in these dozen blocks matters far more than the fact that you landed in Flatiron, the highest-profile submarket in Midtown South.

Office Space for Teams of 5 to 30 People

Many of our clients are teams of 5 to 30 people. The Flatiron headlines this year were AI companies taking big blocks of space: Clay took 163,000 SF at 11 Madison Avenue, and Synthesia moved its headquarters into about 50,000 SF at 675 Avenue of the Americas (Commercial Observer, 2026). Most buildings here are far smaller, and plenty of them lease suites of 1,100 to 5,500 SF.

Plan on about 150 to 250 square feet per person, depending on how many private offices you want. That works out to roughly 750 to 1,250 square feet for 5 people, 2,250 to 3,750 for 15, and 4,500 to 7,500 for 30. Our office space calculator will give you a closer number before you tour.

The side streets between Fifth and Sixth Avenues are where small teams get the most for their money. Suites on our site in October at 19 West 21st, 37 West 20th, and 54 West 21st Streets asked $33 to $56/SF, and 928 Broadway asked $50 to $58/SF. At $55/SF, a 2,000 SF office for about ten people costs about $9,200 a month before electricity. Renovated buildings that AI tenants want have asked $75 to $85/SF this year, including 156 Fifth Avenue and 43 West 23rd Street (Commercial Observer, 2026).

Ask about prebuilt suites. The landlord builds them out before you sign, with private offices, a conference room, and a kitchen, so you can move in within weeks instead of waiting months for construction. When Taconic renovated 61 West 23rd Street, it added prebuilt offices (Commercial Observer, September 2026).

Buildings to start with:

• 19 West 21st Street (Spero Building, between Fifth and Sixth Avenues): a loft building where we listed 1,600 SF on the 3rd floor at $4,400 a month, about $33/SF.
• 37 West 20th Street (between Fifth and Sixth Avenues): we’ve listed suites of 1,125 and 2,103 SF here at about $54 to $56/SF, sizes that suit teams of about 5 to 14 people.
• 54 West 21st Street (between Fifth and Sixth Avenues): a 1,272 SF suite listed at $5,830 a month, about $55/SF. Chalk, the data company, opened its Flatiron office here four years ago before signing for 26,607 SF at 43 West 23rd Street this year (Commercial Observer).
• 928 Broadway: suites of 1,100 and 4,100 SF listed at about $50 to $58/SF, so the same building can work for 5 people or 25.
• 902 Broadway (between 20th and 21st Streets): the Rosen family’s 20-story building, where Industrious signed in February for the entire 7th floor, 18,200 SF, to run as coworking (Commercial Observer).
• 61 West 23rd Street (between Fifth and Sixth Avenues): a seven-story cast-iron building the Zegna family owns, renovated by Taconic with new lobbies, modernized elevators, and prebuilt offices. Full floors run about 8,400 SF, the space Normal Computing is moving into with about 30 people (Commercial Observer).

One deal of ours: in 2023, we moved DFW Capital Partners, a private equity firm relocating from New Jersey, into a 3,000 SF corner suite at 156 Fifth Avenue on a five-year lease. The space came as a white box, and the firm built six offices and a large conference room.

For two to five people, a private office in a coworking space can cost less than a lease of your own.

Flatiron Sub-Areas

Flatiron District Office Market Overview

Tenants who treat Flatiron as one market waste a lot of time. It’s an AI trophy cluster and a value loft district on the same few blocks, and a deal at One Madison Avenue has nothing in common with a deal in a prewar loft off Sixth. Figure out which one you’re shopping before you tour anything, or you’ll lose a month on buildings that were never going to work.

The backdrop is loud. CBRE counts 6.22 million SF of Midtown South leasing through September, the highest year-to-date total on record, and puts district availability at 16.2% (CBRE, Q3 2026). Flatiron is far tighter. CBRE has its Flatiron district at 7.4% available, down a full point in the quarter, and Savills has Flatiron at 7.5%, the second-tightest Manhattan submarket it tracks after Hudson Yards (Savills, Q3 2026). With that little space left, it’s no surprise CBRE says Flatiron’s third-quarter leasing ran behind its usual pace.

Want the proof? Look at who’s signing.

• Ramp, the fintech, expanded to 285,300 SF at 28-40 West 23rd Street, the biggest Midtown South lease of the first quarter and the third-largest in all of Manhattan (The Real Deal, April 2026).
• Clay, an AI sales company that crossed $100 million in revenue, took 163,000 SF at 11 Madison Avenue at $90/SF in March (Commercial Observer, March 9, 2026). In July, Legora, an AI legal-software company, took 98,420 SF there and brought the building to 100% leased (SL Green, July 2026).
• Across the street, Harvey AI doubled down at One Madison Avenue and brought that tower to fully leased too (SL Green, March 2026).

When companies growing this fast commit to ten-year leases at the top of the market, you stop arguing with the chart. For the wider pattern, see our breakdown of the largest Manhattan office leases behind the numbers.

Four Forces to Monitor

• AI reset the top of the market. AI firms have leased about 2.8 million SF in Manhattan this year through September, nearly triple their total for all of 2025 (Cushman & Wakefield, Q3 2026). In Midtown South they signed 58% of all leasing in the third quarter (CBRE, Q3 2026). Clay’s 163,000 SF at 11 Madison landed right here at $90/SF asking (Commercial Observer, March 9, 2026). Every Park Avenue South landlord now points at that number when they sit down to negotiate.
• The good buildings are filling up. One Madison Avenue has been fully leased since March, 11 Madison Avenue filled in July, and BXP’s renovated 360 Park Avenue South followed in September (SL Green, March and July 2026; Commercial Observer, September 22, 2026). If you want a renovated full floor on the east side of Flatiron, the window is closing, and landlords there know it.
• The value side is still cheaper. Savills tracks Flatiron and Park Avenue South as separate submarkets, and in the third quarter the Flatiron piece averaged $67.81/SF against $72.56/SF for Park Avenue South, with just 7.5% of Flatiron space available (Savills, Q3 2026). So the Sixth Avenue side and the prewar side streets still have loft space that rents well below the AI blocks, in the same neighborhood and on the same subway lines. There’s just less of it, so be ready to move. Touring beats averages here.
• Sublet supply keeps shrinking. Manhattan’s sublet supply fell another 12% in the third quarter, to 10.6 million SF, its lowest level since 2019 (Cushman & Wakefield, Q3 2026). If your plan was a cheap Flatiron sublet, most of those dried up in 2024. A few still trade, but you have to move fast.

How Much Does Flatiron District Office Space Cost?

The answer depends on which side of the neighborhood you pick. CBRE’s third-quarter numbers put the Midtown South average at a record $86.94/SF and its Flatiron district at $74.24/SF. On a 3,000 SF office, that $12.70 gap is worth about $38,000 a year, and even the Flatiron average is close to useless on its own, because the spread inside these blocks is enormous. One Madison Avenue asked around $120/SF before it filled. 11 Madison asked $90/SF on Clay’s lease in March. Hex, an AI company out of San Francisco, took a full floor at 250 Park Avenue South at $80/SF (Commercial Observer, January 2026). And on the prewar side streets off Sixth, you can still find office space in the $60s.

So before you tour, answer one question: do you need to be on the AI blocks, or do you just need to be in Flatiron? If you’re a venture-backed AI company competing with OpenAI for talent, you’ll probably pay up for Park Avenue South and Madison Square. If you’re a profitable services firm or a growing startup that wants the neighborhood and the commute without the trophy bill, look west and on the side streets. It’s the same neighborhood and the same trains, at very different rent. Not sure how much space you need? Run your headcount through our Office Space Calculator before you tour anything.

A Quick Note on Building Classifications

If you haven’t shopped Midtown South before, know this up front: the Class A, B, C system doesn’t work here the way it does in Midtown or Downtown. Most of Flatiron’s buildings are converted lofts, former warehouses, and turn-of-the-century cast-iron, not purpose-built office towers. So a 1900s loft on Park Avenue South can technically carry a Class B label and still command rent that beats a Class A tower uptown, because the ceiling height, the light, the floor plate, and the address are what tenants actually pay for. Class describes the building. Rent tier describes what tenants pay. Don’t get hung up on the letter. Our explainer on what makes a building Class A, B, or C breaks it down.

Park Avenue South and the AI Cluster

Park Avenue South is where the change shows most. For a decade it was a solid but unremarkable stretch of lofts. Then the AI companies arrived, and rents reset. The biggest deals of 2025 and 2026 all landed within a few blocks of Madison Square Park. Clay took 163,000 SF at 11 Madison Avenue at $90/SF (Commercial Observer, March 9, 2026), Harvey AI expanded to roughly 185,000 SF at One Madison Avenue, where asking rents ran around $120/SF, and Pinterest and Tempus AI took space at 11 Madison. Smaller AI tenants keep coming too, like Hex at 250 Park Avenue South (Commercial Observer, January 2026). The two anchors, 11 Madison and One Madison, are both owned by SL Green and both fully leased: One Madison since March and 11 Madison since July, when Legora took 98,420 SF (SL Green, 2026).

These are full-block trophy and trophy-adjacent buildings with the amenity packages and the addresses AI flagships want. If you need that kind of space, timing matters more than budget, because these buildings fill faster than they empty. For what actually separates trophy from regular Class A, see our piece on how trophy buildings set themselves apart in NYC. One caveat on geography: 11 Madison and One Madison sit on the Madison Square edge, which the site’s taxonomy also covers under Park Avenue / Madison Square. Different page, same cluster.

Class A and Renovated Loft Space

Step away from the AI blocks and Flatiron is mostly lofts: renovated prewar and cast-iron buildings with high ceilings, big windows, and floor plates that suit a 5,000 to 40,000 SF tenant. This is where most Flatiron leases that aren’t AI megadeals get signed, and there’s a lot to choose from. Many of these landlords have spent heavily on lobbies and prebuilt suites in the last five years, so a renovated loft here often shows better than a glass tower from 2008. The character is the point, and tenants pay for it. The best of this stock spans Fifth Avenue, Broadway, and the blocks around the old Flatiron Building.

One thing to know: the Flatiron Building itself, at 175 Fifth Avenue, is no longer an option. After 120 years as offices, it’s being converted to 38 luxury condominiums, scheduled to finish by year-end (6sqft, 2026). The ground floor will keep retail, including a new restaurant from the team behind Bar Pisellino, but the office floors are gone. If you want the most famous triangular silhouette in America, you’ll have to buy a condo.

Class B and Value Loft Space

The value is on the west side, and a lot of tenants miss it. On the Sixth Avenue side, in the converted Ladies’ Mile department stores, and on the prewar side streets between Fifth and Sixth, Flatiron still has loft space that rents well below Park Avenue South. The submarket averages are closer than you’d think: Savills had Flatiron at $67.81/SF in the third quarter against $72.56/SF for Park Avenue South, and CBRE has both of its districts at about $74 (Q3 2026). Averages blend every building together, though, and the savings show up building by building. You get the same neighborhood and the same trains for noticeably lower rent. This tier works for startups, small and midsize firms, medical and dental practices, nonprofits, and anyone who wants to be in Flatiron without paying AI-cluster rents.

Side-street buildings off Sixth in the West 18th to 22nd Street range carry strong 1,500 to 15,000 SF inventory, and a fair amount of it comes as spec suites you can move into fast. A chunk also trades as sublease, which can be the quickest, cheapest way in if the term fits. Two practical notes before you sign. First, the big brokerages don’t publish a separate Class C average for Flatiron, so anyone who quotes you a single Class C number is guessing. Our value-tier read comes from Metro Manhattan internal research (September 30, 2026). Second, almost every NYC landlord will want a security deposit, and for smaller or newer companies, a Good Guy Guarantee, so understand both before you negotiate. If you’re coming out of a coworking space, our guide to scaling from coworking to your own office walks through it.

Lease Concessions and Effective Rent

Most tenants lose money in the same place. They negotiate the asking rent, win a few dollars, and sign without pushing hard on free rent or the build-out allowance, which is where most of the value is in a Flatiron loft deal. Who pays for the build-out is negotiable, and away from the AI blocks you have more room than you think. The ranges below are typical-market figures from our recent deals (Metro Manhattan internal research, September 30, 2026), assuming a 5 or 10-year term. Shorter terms get smaller packages, and 10- to 15-year terms get bigger ones. CBRE puts the Midtown South average for new raw-space leases at 17 months free and $160.17/SF in build-out money (CBRE, Q3 2026), but that average is driven by large, long-term deals. Small suites get far less, and free rent rarely goes past 12 months. On a 2,500 SF office at Flatiron’s average of about $74/SF, every free month is worth about $15,400.

One more thing: net effective rent usually comes in well below the face rent a landlord first quotes, and knowing how to work it out can turn a fine deal into a great one. Our breakdown of 3-year, 5-year, or 10-year lease terms covers how term length moves the package, and our concessions explainer walks through the effective-rent math.

Which Business Fits the Flatiron District?

Flatiron tenants cluster tightly by industry, and not by accident. AI and fintech want Park Avenue South and Madison Square. Media, creative, and showroom tenants want the lofts off Fifth and Sixth. Smaller firms want the prewar side streets. There’s a reason: your clients, your talent, and the company down the block you want to poach from are already there. Match your industry to the right sub-area, and the search gets a lot smaller. The table below shows the best fits.

Running a lean team? Flatiron isn’t the cheapest corner of Manhattan, and the deepest value is elsewhere. But the side streets off Sixth make sense once you factor in the talent you can recruit by being in the AI neighborhood. Our guide to the top neighborhoods for small businesses lays out the trade-offs. If you want to be near the AI cluster but can’t afford Park Avenue South, AI companies are also leasing in SoHo, Chelsea (where Clay leased before its move to 11 Madison), and even down to the Financial District. Scale AI recently moved there to fit a workforce that doubled to 500 (The Real Deal, 2026).

Top Office Buildings and Amenities in the Flatiron District

If your last Flatiron tour was pre-2020, the picture in your head is wrong. The AI money pulled the amenity game up to Midtown trophy standards, and the best buildings here now compete on lounges and terraces, not just exposed brick. Three tiers to expect:

Trophy and Class A core (11 Madison, One Madison): Tenant-only amenity floors, conferencing, lounges, fitness, rooftop event space, and Madison Square Park views. Marquee on-site dining, with three-Michelin-star Eleven Madison Park at 11 Madison and La Tete d’Or by Daniel Boulud at One Madison. Smart-building systems. It’s the top of Midtown South.

Renovated loft (28-40 West 23rd, 225 Park Avenue South, 122 Fifth Avenue, 200 Fifth Avenue): Restored lobbies, new mechanical systems, on-site fitness and conferencing in the bigger buildings, ground-floor retail, and the high ceilings and natural light that draw tenants to lofts in the first place.

Class B and value loft (71 West 23rd, 113-133 West 18th, side-street prewar stock): Prewar character, big windows, attended lobbies, tenant-controlled HVAC, and a growing number of fully built-out spec suites with furniture and cabling already in place so you can move in fast.

Featured Buildings

• 11 Madison Avenue: SL Green and PGIM’s 2.3M SF, 30-story full-block tower fronting Madison Square Park, the former Metropolitan Life North Building. Clay took 163,000 SF here in March at $90/SF (Commercial Observer, March 9, 2026), and Legora’s 98,420 SF lease brought it to 100% leased in July (SL Green, July 2026). Tenants include UBS, Sony, William Morris Endeavor, Pinterest, and Tempus AI, and Eleven Madison Park sits on the ground floor.
• One Madison Avenue: SL Green’s redeveloped 1.4M SF Class A tower overlooking Madison Square Park, a restored nine-story podium under a new tower. Harvey AI expanded to roughly 185,000 SF here in Q1 2026, filling the building (SL Green, March 2026). Asking rents were around $120/SF. Amenities include a rooftop event space, La Tete d’Or by Daniel Boulud, and Chelsea Piers Fitness.
• 28-40 West 23rd Street: Williams Equities’ two-building, 561,000 SF complex between Fifth and Sixth, the old Home Depot building. Fintech Ramp anchors it after expanding to 285,300 SF in Q1 2026, the largest Midtown South lease of the first quarter (The Real Deal, April 2026). Renovated lobbies, new cooling towers, and a planned roof deck.
• 225 Park Avenue South (American Woolen Building): A 19-story prewar loft at Park Avenue South and 18th Street, two blocks above Union Square. It lost Meta and sat heavily vacant in 2024. In late 2025, Monday.com, which opened its North American headquarters here in 2022, renewed for 10 years and grew to 138,611 SF (Commercial Observer, December 2025).
• The Flatiron Building (175 Fifth Avenue): The 1902 Beaux-Arts landmark by Daniel Burnham, one of the world’s first skyscrapers. After 120 years as offices, the Brodsky Organization, GFP Real Estate, and Sorgente Group are converting it to 38 luxury condominiums, scheduled to finish by year-end (6sqft, 2026). It’s no longer leasable office space, but it still gives the neighborhood its name.
• 122 Fifth Avenue: Bromley Companies’ modern Flatiron development, where Microsoft leases roughly half the building. A rare new-construction option in a neighborhood built on conversions.

Ground-floor and flagship retail space along Fifth Avenue, Broadway, and the Ladies’ Mile stretch of Sixth is some of the highest-traffic retail in the neighborhood. If you’re after a storefront rather than a floor upstairs, that’s a different search, and a very good one here.

Major Office Landlords in the Flatiron District

Who owns your building matters as much as which building you pick, because every major Flatiron landlord negotiates differently. SL Green, the city’s largest office landlord, owns both Madison Square anchors, filled both of them this year, and posted its best first quarter in 28 years, so it’s dealing from strength and pushing hard (SL Green, March and July 2026). Williams Equities holds the Ramp building and runs a tight, well-capitalized shop. Smaller owners like Olmstead, Feil, and Bromley are aggressive on the Park Avenue South side and will move quickly for the right tenant. A good broker knows what you’re walking into. For background, see our overview of the biggest commercial real estate landlords in NYC. Several of these owners also hold much larger portfolios in Downtown Manhattan, where the same dollar buys more space.

Transportation and Commuting to the Flatiron District

Flatiron sits right in the center of Manhattan, which makes it a faster commute from almost everywhere than your team probably realizes. Union Square anchors the south end with eight subway lines, the 23rd Street stations cover the core, PATH runs to New Jersey, and Penn Station and Grand Central are both a short hop away. If anyone on your team is resisting the commute, send them our Commute Calculator with their home address. The numbers usually make the case.