Floor Plan Square Footage Calculator
Calculate floor plan square footage by measuring each room separately and summing the totals. Use the multi-segment tool to add all rooms in one calculation.
Floor Plan Calculator
Room-by-room measuring
For an existing home: measure each room's interior dimensions and label them on a floor plan sketch. Sum all rooms, then add hallway and stair landing areas.
A typical 3-bedroom 2-bath ranch has: living room (~250 sq ft), kitchen (~200), dining (~150), 3 bedrooms (~150 each), 2 bathrooms (~50 each), hallways (~80) = roughly 1,330 sq ft of interior + walls = 1,500-1,600 sq ft gross.
Interior vs. gross floor area
Adding up interior room dimensions gives you "carpetable" or net floor area. The official ANSI Z765 square footage measures to the exterior wall surface and includes the walls themselves.
The difference between interior-only and gross-with-walls is typically 10-12% for residential construction. A house with 1,500 sq ft of net interior space usually has 1,650-1,700 sq ft of ANSI gross.
Pro tips
Use blueprints if available
Architectural drawings list room dimensions and total square footage. Cross-check the blueprint number against your physical measurement.
Don't double count walls
When adding room areas to get a total, you're measuring interior area only. Don't also add the wall thickness - that comes out automatically when measuring exterior to exterior.
Stairs count once
A staircase counts as floor area on the lower floor only - the upper-floor "open to below" doesn't count.
Closets are part of the room
For interior measurement, closets are usually included with the bedroom. For ANSI gross, they're part of the building footprint.