Square Footage Calculator
Square feet = length × width, in feet. A 12 × 10 ft room is 120 ft² (11.15 m², 13.33 yd²); for an L-shaped room, split it into rectangles, circles or triangles and add them.
Area
120 ft²
11.15 m² · 13.33 yd²
- Area 1
- 120 ft²
How it works
Rectangle: area = length × width
Circle: area = π × diameter² ÷ 4
Triangle: area = base × height ÷ 2
Feet and inches: feet + inches ÷ 12 (12 ft 6 in = 12.5 ft)
1 yd² = 9 ft² · 1 ft² = 0.09290304 m²
Assumptions
- Each shape is measured on the floor plan (flat, horizontal area).
- For an L-shaped or irregular room, split it into rectangles and triangles and add them; do not overlap the pieces. ENERGY STAR describes the same method.
- A triangle's height is measured at a right angle to its base, not along a slanted side.
Worked examples
Two rooms, one measured in feet and inches
- Room 1: 12 ft × 10 ft = 120 ft²
- Room 2: 10 ft 6 in = 10.5 ft, so 10.5 × 9 = 94.5 ft²
- Total: 120 + 94.5 = 214.5 ft²
Result: 214.5 ft² (19.93 m², 23.83 yd²).
Checked by the automated test “square footage — two rooms with feet and inches add up to 214.5 ft²”.
One floor of a 28 × 42 ft house
- 28 × 42 = 1,176 ft²
Result: 1,176 ft², the figure used as an example in the ANSI Z765 square-footage standard.
Checked by the automated test “square footage — 28 × 42 ft = 1,176 ft² (ANSI Z765 example)”.
Buying material by the square foot
- The calculator gives the exact area. Flooring, tile and sod are sold with a cutting allowance on top: add the percentage the maker recommends for your layout, since diagonal patterns waste more than straight ones.
- Round boxes up. Divide the area plus allowance by the coverage printed on one box, and round up to whole boxes.
- Keep the room list. Each area stays on its own line, so you can reuse the same numbers for paint or baseboard estimates.
Common mistakes
- Measuring above the baseboard. For flooring, measure wall to wall at floor level; trim hides the gap at the edge.
- Stretching a room to include a closet. Add the closet as its own rectangle, and only if the material goes in it.
- Measuring a triangle along its slanted side. For bay windows and angled corners, take the base along the main wall and the depth straight out from it.
Frequently asked questions
How do I calculate the square footage of a room?
Multiply the length by the width, both in feet. A 12 × 10 ft room is 120 ft². If a measurement has inches, divide them by 12 first (6 in = 0.5 ft) or type them in the inch box.
How do I figure square yards?
Divide square feet by 9, since a square yard is 3 ft × 3 ft. The 120 ft² room is 13.33 yd²; the calculator shows square yards under every total.
Is the square footage of a house the sum of its rooms?
No. Under ANSI Z765, the standard used for real-estate square footage, finished area is measured from the outside walls and includes walls, halls and stairs. It is larger than the total of the room floors you measure inside.
How many square feet are in an acre?
43,560 ft² (4,046.86 m²), per NIST. You can check it here: a 660 × 66 ft rectangle is exactly 43,560 ft². To convert a lot size to acres, divide its square feet by 43,560.
Sources
Formula, examples and sources checked on by the Yardstick Math team. How we check our formulas.
- Room Air Conditioners – Determine the room's square footage — ENERGY STAR (US EPA)
- ANSI Z765-2021 Square Footage – Method for Calculating (§3.2 exterior finished surface; 28 × 42 ft example) — Home Innovation Research Labs / ANSI (copy hosted by NWMLS)
- U.S. Survey Foot: Revised Unit Conversion Factors (acre = 43,560 ft²) — NIST
- Handbook 44, Appendix C – General Tables of Units of Measurement — NIST