How to use it
- Choose feet and inches or meters, pick a shape for each area and enter its measurements. Use a quantity for repeated areas, such as three identical bedrooms.
- Tick Subtract for parts to leave out: a fireplace hearth, a kitchen island, a stair opening.
- Read the total in square feet, square meters, square yards and acres; add an extra percentage for cuts and a price per square foot or meter for a cost estimate.
How it calculates
Every measurement is converted to feet (inches ÷ 12, meters ÷ 0.3048, the exact international definition of the foot) and each area worked out with the usual formula: length × width, base × height ÷ 2, π × diameter² ÷ 4, or the trapezoid’s average width × height. Areas are multiplied by their quantity, subtracted where ticked, and added. Square meters use 0.3048² = 0.09290304 m² per square foot, square yards 9 square feet and acres 43,560 square feet.
What we tested
On October 14, 2026 we compared the page’s own functions with exact fractions (and a 40-digit value of π for circles) on 3,001 random sets of up to five areas in feet and inches or meters, with quantities and subtractions: every total in square feet, square meters, square yards and acres matched, the largest relative difference being 1.5e-13. A version using 0.305 m for a foot instead of 0.3048 failed the metric cases. In Chromium: the default L-shaped room (14 ft 6 in × 12 ft plus an 8 × 5 ft alcove, less a 3 × 2 ft hearth) showed 208.00 sq ft, 19.32 m² and 23.11 sq yd; adding a 10 ft circle added 78.54 sq ft for 286.54; 10% extra at $4.50 showed 315.19 sq ft and $1,418.37; a negative length showed a message; switching to meters re-read the numbers as meters; the page fitted a 390 px phone with no errors.
| Example | Result |
|---|---|
| 14 ft 6 in × 12 ft | 174 sq ft |
| + 8 × 5 ft alcove − 3 × 2 ft hearth | 208 sq ft = 19.32 m² = 23.11 sq yd |
| 10 ft diameter circle | 78.54 sq ft |
For other unit conversions, see the Measurement Unit Converter.
Frequently Asked Questions
Built by Derek Giordano · Part of Ultimate Design Tools