How to calculate square footage
By Dexaloop · Updated 27 October 2026 · Checked against the sources listed below
To calculate square footage, measure the length and width in feet and multiply them: a floor 12 feet by 10 feet is 120 square feet. If a measurement has inches, divide the inches by 12 first, so 10 feet 6 inches becomes 10.5 feet. For shapes that are not rectangles, break them into rectangles, triangles and circles, work out each one, and add them up. This guide shows the formula for each shape, how to handle L-shaped rooms, and how to convert between square inches, square feet, square yards and square meters without rounding errors.
The one rule behind every area sum
Area is always one length multiplied by another length in the same unit. Feet times feet gives square feet. Inches times inches gives square inches. Most mistakes come from mixing units, such as multiplying 12 feet by 8 inches. So before you multiply anything, convert every measurement to one unit, usually decimal feet.
| Inches | Decimal feet |
|---|---|
| 1 | 0.083 |
| 3 | 0.25 |
| 4 | 0.333 |
| 6 | 0.5 |
| 8 | 0.667 |
| 9 | 0.75 |
A common slip is writing 12 feet 6 inches as 12.6. It is 12.5, because 6 inches is half of 12, not six tenths of a foot.
Formulas for each shape
| Shape | Formula | What to measure |
|---|---|---|
| Rectangle or square | length x width | Two sides that meet at a corner |
| Triangle | base x height / 2 | Height at a right angle to the base, not the sloping side |
| Circle | 3.1416 x radius x radius | Radius is half the distance across |
| Half circle | 3.1416 x radius x radius / 2 | Radius is half the straight side |
| Trapezoid (two parallel sides) | (side a + side b) / 2 x height | Height between the parallel sides |
Worked example: a rectangular room
A bedroom measures 14 ft 9 in by 11 ft 4 in.
- 14 ft 9 in = 14 + 9/12 = 14.75 ft.
- 11 ft 4 in = 11 + 4/12 = 11.333 ft.
- 14.75 x 11.333 = 167.17 square feet.
Keep at least three decimal places until the last step. Rounding 11.333 to 11.3 would lose about half a square foot here, and more on a larger floor.
Worked example: an L-shaped room
Picture a room whose outer edges are 20 ft by 16 ft, with an 8 ft by 6 ft corner missing where a closet sits. There are two ways to get the area, and doing both is a good check.
Subtract method. Treat it as the full rectangle and take away the missing piece: 20 x 16 = 320, minus 8 x 6 = 48, gives 272 square feet.
Split method. Cut it into two rectangles that do not overlap. The full-width part is 20 ft by 10 ft = 200. The narrower part is 12 ft by 6 ft = 72. Total: 272 square feet.
If the two methods disagree, one of your measurements is wrong. The most common cause is counting the overlap twice, by measuring both rectangles to the outer wall.
Worked example: triangles and circles
Angled corner. A room has a corner cut off at an angle, leaving a triangle with a base of 12 ft and a height of 7 ft measured straight out from the base. Its area is 12 x 7 / 2 = 42 square feet. If you measured the sloping edge instead of the straight height, the answer would be too large.
Round patio. A patio is 10 ft across, so its radius is 5 ft. Area = 3.1416 x 5 x 5 = 78.54 square feet. A half-round bay with a 10 ft straight side is half of that, 39.27 square feet.
For a curve that is not a true circle, measure it as a few short straight sections, or draw it on graph paper and count squares. Small errors on a curved edge rarely change a materials order by much.
Converting between units
NIST Handbook 44, the US reference for units used in trade, lists these relationships. The ones marked exact are definitions, not roundings.
| From | To | Do this | NIST basis |
|---|---|---|---|
| Square inches | Square feet | divide by 144 | 1 sq ft = 144 square inches (exactly) |
| Square feet | Square yards | divide by 9 | 1 sq yd = 9 square feet (exactly) |
| Square feet | Square meters | multiply by 0.09290304 | 1 foot = 0.3048 meter exactly, squared |
| Square meters | Square feet | multiply by about 10.764 | 1 m² = about 10.764 square feet (NIST: 10.763 91) |
| Square feet | Acres | divide by 43,560 | 1 acre = 43 560 square feet |
Square inches example. A countertop is 96 in by 25.5 in. That is 96 x 25.5 = 2,448 square inches. Divided by 144 it is exactly 17 square feet.
Metric example. A room measured as 4.2 m by 3.6 m is 15.12 m². Times 10.764 that is 162.75 square feet. Going back, the 272 sq ft L-shaped room is 272 x 0.09290304 = 25.27 m².
Square yards example. The same 272 sq ft room is 272 / 9 = 30.22 square yards.
Do not divide square feet by 3 to get square yards. Three is the factor for length (3 feet in a yard). For area you divide by 3 x 3 = 9.
How to measure so the sum is right
- Measure wall to wall at floor level, where flooring will actually go.
- Measure each wall, not just one of each pair. Rooms are often a little out of square, and the longer reading is the safer one for ordering.
- Sketch the floor plan and write each measurement on it before you do any sums.
- Decide what to include. Closets and alcoves usually count for flooring; a kitchen island or fixed cabinets usually do not.
- For a whole home, add each room separately rather than measuring the outside of the house, which includes walls.
Common mistakes
- Writing inches as tenths. 8 ft 6 in is 8.5 ft, not 8.6.
- Mixing feet and inches in one multiplication. Convert first.
- Using the diameter as the radius. That makes a circle four times too big.
- Using the slope of a triangle as its height. Height is measured square to the base.
- Counting the overlap twice in an L-shape. Check with the subtract method.
- Dividing by 3 for square yards. Divide by 9.
- Rounding too early. Keep decimals until the final answer.
Once you have the area, buy material by how it is actually sold: by the box for flooring, by the square yard for some carpet, by the gallon for paint. The calculator below adds several shapes at once and shows square feet, square yards and square meters together.
Add up the areas: tools.dexaloop.com/square-footage-calculator/. Free, no sign-up, and it runs on your device.
Questions
How do I calculate square footage of a room?
Measure the length and width in feet, turn any inches into decimal feet by dividing by 12, and multiply. A room 14 ft 9 in by 11 ft 4 in is 14.75 x 11.333 = 167.17 square feet.
How do I find the square footage of an L-shaped room?
Either split it into two rectangles that do not overlap and add them, or measure the full rectangle around it and subtract the missing corner. Both give the same answer if the measurements are right.
How do I convert square inches to square feet?
Divide by 144, because NIST lists one square foot as exactly 144 square inches (12 x 12).
How do I convert square meters to square feet?
Multiply by about 10.764 (NIST lists 10.763 91). To go the other way, multiply square feet by 0.09290304, which comes from the exact definition of the foot as 0.3048 meter.
How many square feet are in a square yard?
Nine. A square yard is 3 feet by 3 feet. Divide square feet by 9 to get square yards, which is how carpet is often priced.
How many square feet are in an acre?
NIST lists an acre as 43,560 square feet. A quarter-acre lot is 10,890 square feet.
Sources
This guide is general information, not legal, tax or financial advice. Rules change; check the official source for your own case. Found a mistake? Email support@dexaloop.com.
Related tools
- Flooring calculator
- Feet and inches calculator
- Paint calculator
- Guide: how to measure a room for flooring