The number
nobody measures alike
Ask three sources an apartment's size and receive three answers — sometimes fifteen percent apart. The measurement chaos is structural; the honest comparison method survives it.
Before you read on
- General information as of August 2026.
- No single measurement standard governs NYC residential — the chaos is the system.
- The comparison method in Section 3 is the practical takeaway.
Point 1Why the numbers diverge
The measurement anarchy's sources: offering plans measure to exterior walls and include share-of-common allocations (the developer's generous convention — the number your price-per-foot was marketed on), architects and appraisers measure interior usable space (the smaller truth), co-ops often publish no square footage at all (shares, not feet, being the legal unit), and listing figures inherit whichever ancestor served best.
The scale of divergence: exterior-wall conventions run five-to-fifteen percent above interior-usable on the same apartment — the 1,000-foot condo of the offering plan living as 870 usable feet. Neither number is fraudulent; they answer different questions under different customs. The buyer's error is comparing across conventions unknowingly.
Point 2The customs by context
The legal reality behind the disclaimers: New York contracts sell the apartment as-is-where-is, square footage 'approximate' and non-warranted — litigation over size shortfalls fails except in egregious misrepresentation. The number is marketing context, not contractual substance; the walk-through and floor plan are the substance.
| Source | Convention | Bias |
|---|---|---|
| Offering plans (condos) | Exterior walls + allocations | The largest number |
| Listings | Inherited/optimistic | Unverifiable without asking |
| Appraisals | Interior measurements | Smaller, consistent |
| Co-op listings | Often none published | Shares and rooms instead |
| Floor plans' dimensions | Room-by-room, summable | Your verification tool |
| Property records | Sporadic and dated | Weak authority |
'Approximately' before any figure is doing heavy legal lifting — contracts disclaim square footage almost universally.
Point 3Comparing honestly anyway
The method that survives the chaos: compare within conventions (offering-plan numbers against offering-plan numbers — same-building comparisons are automatically clean), verify with floor plans (room dimensions summable into your own consistent figure — the fifteen-minute exercise for any serious candidate), and weight layouts over totals (the efficient 850 beating the corridor-wasted 1,000 in lived and resale reality — the layout chapters' recurring lesson).
Price-per-foot's honest use follows: within-building and within-convention comparisons illuminate; cross-convention comparisons mislead by exactly the measurement gap. The reports chapter's per-foot analytics inherit the same caveat — segment and convention discipline before arithmetic.
Point 4Where the number matters most
The moments demanding measurement care: renovation budgeting (contractors bid on actual measured space — the budgeting chapter's estimates want architect's figures, not marketing's), furniture and planning (the interior truth again), appraisal season (the lender's smaller number driving loan math the financing chapters warn about), and rentals (tenants comparing your listing against others inherit the same chaos — honest figures with floor plans rent better than optimistic ones that disappoint at viewings).
The buyer's settled posture: collect the offering plan's number for context, sum the floor plan yourself for truth, compare within conventions, and let layout quality outrank totals — then never argue about square footage again. In a market where the number lies structurally, the buyers who measure once and move on hold the only defensible relationship with it.
Different conventions: offering plans measure exterior walls plus allocations; appraisers measure interior usable space — five-to-fifteen percent gaps are normal, not fraud.
Almost never successfully — contracts disclaim the figure as approximate and non-warranted. The floor plan and walk-through are the substance; the number is context.
Sum the floor plan's room dimensions yourself — fifteen minutes to a consistent figure — or commission measurement for renovation-grade truth.
Shares are the legal unit, and the custom persists — rooms and layouts carry co-op listings. The comparison method adapts: floor plans and within-building comps.
Within conventions and buildings it illuminates; across conventions it misleads by the measurement gap. Segment discipline first, arithmetic second.
Appraisals use interior measurements — the smaller number feeding loan math. The financing chapters' appraisal-gap planning includes exactly this.
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Important notice
The figures on this page are general information as of August 2026 and do not represent an offer, a quote, or a guarantee of any transaction terms. Reinvent NY does not provide legal, tax, or investment advice. Confirm anything material with an attorney and a CPA before you act on it. Nothing here is a solicitation to invest, and no return is promised. Real estate brokerage services are provided through R New York.