Almost every home project starts with square footage: flooring, paint, sod, pavers, roofing, even pricing a room addition. Real spaces are rarely a single rectangle, though, so this square footage calculator lets you add as many sections as you need. Break an L-shaped room, a yard with a curved bed or a house with a bay window into rectangles, triangles and circles, enter each one, and the calculator totals them in square feet, square metres, square yards and acres.
Once you have the total, feed it into the flooring calculator, the sod calculator or the paver calculator to turn area into materials.
How to use the square footage calculator
- Sketch the space and split it into simple shapes. An L-shaped room is two rectangles; a bay window is often a rectangle plus a triangle or two.
- Add a row for each section, choose its shape and enter its dimensions. Rectangles take length and width, triangles base and height (perpendicular to the base), circles the diameter.
- Select the unit you measured in. All sections must use the same unit.
- Read the total in square feet and the conversions to m², yd² and acres.
- Optionally enter a price per square foot to estimate the cost of flooring, sod or another material priced by area.
Formula
Conversions use the exact definitions published by NIST: 1 ft = 0.3048 m, 1 yd² = 9 ft², 1 acre = 43,560 ft². For a half-circle, enter the full diameter and halve the result, or use a triangle and rectangle approximation.
Worked example
An open-plan living area: a 15 × 18 ft living room, a 12 × 10 ft kitchen and a triangular bay window 6 ft wide and 4 ft deep.
- Living room: 15 × 18 = 270 ft².
- Kitchen: 12 × 10 = 120 ft².
- Bay: 6 × 4 ÷ 2 = 12 ft².
- Total: 270 + 120 + 12 = 402 ft² = 37.35 m² = 44.67 yd².
- At $4.50 per ft² for flooring: 402 × 4.50 = $1,809.
Measuring tips
- Measure wall to wall at floor level, and round up to the next inch. Small errors multiply: being 2 inches short on both sides of a 12 × 12 room understates the area by about 4 ft².
- For flooring, include closets and the space under built-ins that will get the new floor. For paint, measure walls instead (perimeter × height); the paint calculator does this for you.
- For yards and lawns, use a measuring wheel or the measuring tool in an online map, then check a couple of dimensions on the ground.
- For triangles, the height must be measured at a right angle to the base, not along the sloping side.
Square footage of a house
Listing and appraisal square footage follows specific rules that differ from simply adding room areas. In the U.S., ANSI Z765 (published by the Home Innovation Research Labs) is a widely used standard for measuring single-family homes: it measures finished area at floor level to the exterior finished wall surface, reports above-grade and below-grade areas separately, and excludes garages and unfinished areas; finished space generally needs a ceiling height of at least 7 ft. If you need the official figure for a sale or appraisal, use that standard or ask your appraiser.
Caveats and assumptions
- All sections must be measured in the same unit.
- Triangles use base × height ÷ 2, where height is perpendicular to the base.
- For materials, add a waste allowance to the area; this calculator gives net area only.
- Area for real-estate listings follows standards such as ANSI Z765 and may differ from a room-by-room total.
Frequently asked questions
How do I calculate square footage?
Multiply length by width in feet. For irregular spaces, split them into rectangles, triangles and circles, calculate each and add them up.
How do I find the square footage of an L-shaped room?
Divide it into two rectangles that do not overlap, multiply length × width for each, and add the two areas.
How many square feet is a 12 × 12 room?
144 ft², which is 13.38 m² or 16 yd².
How do I convert square feet to square metres?
Multiply by 0.09290304. To go the other way, multiply square metres by 10.764.
How many square feet are in an acre?
43,560 ft². A quarter-acre lot is 10,890 ft².
Sources
- NIST — Unit Conversion — foot, metre, yard and acre definitions
- Home Innovation Research Labs — ANSI Z765 Square Footage Method for Calculating — standard for measuring house area
This calculator gives estimates for planning and education. Check measurements, local codes, supplier specs and your school's official policy before relying on a result. See our disclaimer and how we build and check calculators.