Square Footage Calculator

How to use the square footage calculator

1. Pick the shape. Use “Rectangle in feet + inches” if your tape measure reads something like 15 ft 6 in.
2. Choose the unit you measured in: feet, inches, yards, metres or centimetres.
3. Enter the dimensions. For an L-shaped room, split it into two rectangles that do not overlap.
4. For a whole floor or house, choose Several rooms and type one room per line, such as Bedroom: 12 x 11 or Kitchen: 10' 6" x 9'.
5. Optionally add a waste allowance and a price per square foot, square metre or square yard.

You get the area in square feet, square metres, square yards and acres, the working for each step and, if you entered a price, the estimated cost.

Square footage formulas

Shape	Formula
Rectangle or square	length × width
L-shape	(length A × width A) + (length B × width B)
Circle	π × radius², where radius = diameter ÷ 2
Triangle	½ × base × height
Trapezoid	(side a + side b) ÷ 2 × height

Always multiply two measurements in the same unit. If you measured in inches, divide square inches by 144 to get square feet. If you measured in metres, multiply square metres by 10.7639.

Worked examples

Area	Measurements	Square feet
Bedroom	15 ft × 12 ft	180
Living room	15 ft 6 in × 12 ft 3 in	189.88
L-shaped room	(20 × 12) + (10 × 8) ft	320
Round patio	10 ft diameter	78.54
Triangular garden bed	base 10 ft, height 8 ft	40
Trapezoid lot corner	sides 10 and 14 ft, 8 ft apart	96
Metric room	5 m × 4 m (20 m²)	215.28

The default list in the calculator shows how a multi-room total works: a 15 × 12 living room (180 sq ft), a 12 × 11 bedroom (132 sq ft) and a 10’ 6” × 9’ kitchen (94.5 sq ft) add up to 406.5 sq ft, or 37.77 m².

Square footage for flooring, tile and paint

Buy more material than the floor area. Cuts at walls, pattern matching and broken pieces all use extra:

• Straight-lay flooring and carpet: add 5% to 10%.
• Tile on a diagonal or herringbone: add 15% or more.
• Small or oddly shaped rooms: add more, because a larger share of each piece is cut off.

For example, a 15 × 12 ft bedroom is 180 sq ft. With 10% waste you need 198 sq ft, and at $4.50 per square foot the flooring costs about $891. Carpet is often priced per square yard, and 180 sq ft is 20 sq yd. Switch the price unit to match the quote you have.

For walls, measure each wall’s width by the ceiling height and subtract doors and windows. To figure out how much concrete a slab needs, use the concrete calculator, which takes thickness into account.

How to measure square footage of a house

Measure each room wall to wall and add them with the list option, or measure the outside of the house and subtract anything that is not living space. In the U.S., appraisers and builders commonly follow the ANSI Z765 standard, which counts finished, above-grade living area measured from the exterior walls and reports garages, unfinished basements and open porches separately. That is why a listing’s square footage is usually larger than the sum of the rooms inside it: wall thickness, hallways and closets all count. If you are comparing homes by price per square foot, make sure both numbers were measured the same way. The home affordability calculator helps you see what price range fits your budget.

Measuring irregular shapes

Most irregular rooms can be broken into rectangles, triangles and part-circles. Sketch the floor plan, draw lines to split it into simple shapes, measure each one, and add the areas. Subtract any shape that is cut out, such as a chimney breast or a built-in cabinet you will not floor around. For a bay window, treat the bay as a trapezoid. For curved edges, a circle’s area divided by 2 (a semicircle) or 4 (a quarter-circle) is usually close enough. The general area calculator covers more shapes, such as ellipses and sectors.

Area unit conversions

Unit	Square feet
1 square yard	9
1 square metre	10.7639
1 acre	43,560
1 hectare	107,639