How to calculate square footage
Square footage is the area of a flat surface in square feet. For a rectangle, multiply the length by the width, both in feet.
square yards = square feet ÷ 9
square meters = square feet × 0.09290304
A square yard is 3 ft × 3 ft, so it holds 9 square feet. An acre is 43,560 square feet. A foot is defined as exactly 0.3048 m, so a square foot is exactly 0.09290304 m².[1][2]
Measuring a room
- Measure at the floor, wall to wall. Run the tape along the floor, not along the top of the baseboard, and round each measurement up to the next inch. Walls are rarely straight, so measure each room in two places and use the longer figure.
- Write feet and inches as feet and inches. The calculator reads 12'6", 12 ft 6 in, 6 1/2 and ½, so you can type what the tape says. A phone’s number pad has no ' or / keys; there, type 12.5 for 12 ft 6 in. If you convert by hand, 6 inches is 0.5 ft, not 0.6 ft.
- Break the floor into rectangles. An L-shaped room is two rectangles. Draw the room, cut it into pieces that do not overlap, and add each piece as its own area.
- Add closets, alcoves and bay windows separately if the flooring runs into them. A closet with a door is easy to forget and often gets the same floor.
- Subtract what you will not cover. A kitchen island, a fireplace hearth or a built-in cabinet sits on the subfloor. Add it as another area and tick “Subtract this area”.
Example: an L-shaped living room in feet and inches
The main part of the room measures 12 ft 6 in by 11 ft, and a nook on one side is 6 ft by 2 ft.
- Main part: 12'6" = 12.5 ft, so 12.5 × 11 = 137.50 sq ft
- Nook: 6 × 2 = 12.00 sq ft
- Total: 137.50 + 12.00 = 149.50 sq ft (16.61 sq yd, 13.89 m²)
Typing 12.6 for 12'6" is a common slip. It gives 12.6 × 11 = 138.60 sq ft for the main part, 1.10 sq ft too much.
Example: a kitchen with an island and a pantry
The kitchen is 14 × 12 ft, the island is 6 × 3 ft, and the floor continues into a pantry 6½ ft by 2 ft.
- Kitchen: 14 × 12 = 168.00 sq ft
- Island, subtracted: 6 × 3 = 18.00 sq ft
- Pantry: 6.5 × 2 = 13.00 sq ft
- Total: 168.00 − 18.00 + 13.00 = 163.00 sq ft
Leave the island in if the new floor will run under it. Whether it should depends on the flooring and how it is installed, so check the flooring maker’s instructions before you subtract.
Area formulas for other shapes
The calculator has these shapes. Pick one for each area and mix them in one takeoff.
| Shape | Formula | Example | Area |
|---|---|---|---|
| Rectangle | length × width | 12 × 10 ft | 120.00 sq ft |
| Triangle | base × height ÷ 2 | base 10 ft, height 8 ft | 40.00 sq ft |
| Circle | π × (diameter ÷ 2)² | 10 ft across | 78.54 sq ft |
| Trapezoid | (top width + bottom width) ÷ 2 × length | 6 and 10 ft wide, 8 ft long | 64.00 sq ft |
| Ring | π × ((outer ÷ 2)² − (inner ÷ 2)²) | 12 ft outside, 4 ft inside | 100.53 sq ft |
The triangle’s height is measured square to the base, not along a sloping side. A room with one angled wall is a rectangle plus a triangle, or a single trapezoid if the two parallel walls are the ends.
Square feet, square yards, square meters and acres
All conversions use the exact definitions above.[1][2]
| Size | Square feet | Square yards | Square meters | Acres |
|---|---|---|---|---|
| 10 × 10 ft | 100 | 11.11 | 9.29 | 0.0023 |
| 12 × 12 ft | 144 | 16.00 | 13.38 | 0.0033 |
| 12 × 15 ft | 180 | 20.00 | 16.72 | 0.0041 |
| 20 × 20 ft | 400 | 44.44 | 37.16 | 0.0092 |
| 30 × 40 ft | 1,200 | 133.33 | 111.48 | 0.0275 |
| 50 × 100 ft | 5,000 | 555.56 | 464.52 | 0.1148 |
| 1 acre | 43,560 | 4,840 | 4,046.86 | 1 |
Buying flooring: extra and whole boxes
The area you measured is not the amount to buy. Tile, plank and sheet flooring lose material at every wall and doorway where a piece is cut, and some cut-offs are too short to reuse. How much extra depends on the material, the size of the pieces and the layout: a diagonal or herringbone pattern wastes more than a straight lay. That is why the extra field starts at 0. Use the figure from the flooring maker’s instructions or your installer, or use the tile calculator, which works from the tile size and layout.
Flooring is sold in whole boxes, so the count always rounds up. Enter the coverage printed on the carton and the calculator adds the extra first, then divides and rounds up. For the L-shaped room above with a carton marked 22 sq ft (check your own carton), 149.50 ÷ 22 = 6.80, so you buy 7 boxes before any extra. If the cartons carry a lot or run number, buy them all from the same one so the color matches.
Carpet is often priced by the square yard
Carpet is often priced per square yard rather than per square foot, so divide the area by 9 before comparing prices: the 144 sq ft of a 12 × 12 ft room is 16.00 sq yd. Set “Priced per” to square yard and the calculator converts for you. Carpet also comes off a roll of a fixed width, so the amount you order is usually more than the floor area once seams and the direction of the pile are planned. The carpet calculator lays out the roll strips for you.
A room takeoff is not the house’s listed square footage
The square footage in a home listing or appraisal is measured under its own rules. Fannie Mae directs appraisers to follow the ANSI Z765-2021 standard when they measure single-family homes.[3] That figure is not the same as the floor you are covering, so don’t expect the sum of your room measurements to match it. For flooring, paint or any material, measure the surfaces you will actually cover.
Questions people ask
How do I calculate sq ft?
Measure the length and width in feet and multiply them. Convert inches to feet by dividing by 12 first (6 in = 0.5 ft). For an odd-shaped room, split it into rectangles and add them.
How many sq ft is in a 12x12 room?
144 sq ft (12 × 12), which is 16.00 square yards or 13.38 square meters.
How many sq ft is 30x40?
1,200 sq ft (30 × 40), or 133.33 square yards and 0.0275 acres.
How much flooring is needed for a 12x12 room?
The floor is 144 sq ft. Add the extra for cuts that the flooring maker or your installer recommends, divide by the coverage on the box and round up to whole boxes.
How many yards of carpet do I need for a 12x12 room?
The floor area is 16.00 square yards (144 ÷ 9). The amount to order depends on the roll width and where the seams go, so it can be more; the carpet calculator works it out from the roll.
Related calculators
Sources
- NIST, Handbook 44 (2024), Appendix C: General Tables of Units of Measurement. Units of area: 1 square yard = 9 square feet; 1 acre = 43 560 square feet; 1 square foot = 0.092 903 04 square meter. Checked 2026-10-05.
- NIST, Guide to the SI (SP 811), Appendix B.9: conversion factors by kind of quantity. Square foot to square meter 9.290 304 E-02, shown in boldface (exact). Checked 2026-10-05.
- Fannie Mae, Selling Guide B4-1.3-05, Improvements Section of the Appraisal Report. Appraisers follow ANSI Z765-2021 when measuring and reporting square footage of single-family dwellings. Checked 2026-10-05.