To calculate square footage, by hand or with our square footage calculator, multiply the length by the width, both in feet. A room that is 12 ft long and 10 ft wide is 12 x 10 = 120 sq ft. For an L-shaped or irregular room, split it into rectangles, work out each area, and add them together.
Enter up to three areas below. The calculator adds them up and converts the total to square yards and square meters.
In this guide
How to measure square footage
- Sketch the space. Draw a rough outline of the room, including closets, alcoves, and bump-outs. You will write your measurements on it.
- Divide it into rectangles. Draw lines to split any L-shape, T-shape, or offset into rectangles that do not overlap. Most rooms need one to three.
- Measure each rectangle. Run the tape wall to wall along the floor for the length, then the width. Measure to the nearest inch.
- Convert inches to decimal feet. Divide the inches by 12. Ten feet 6 inches is 10.5 ft, not 10.6 ft. The table below does this for you.
- Multiply and add. Length x width for each rectangle, then add the results. Enter each rectangle as an area in the calculator.
- Round up for buying materials. The calculator shows whole square feet. When you order material, add the waste allowance the product needs.
The formula (with worked examples)
- Rectangle: area = length x width
- Several rectangles: total = (length 1 x width 1) + (length 2 x width 2) + (length 3 x width 3)
- Square yards = square feet / 9
- Square meters = square feet x 0.092903
Example 1: the calculator defaults
The default is one 12 x 10 ft area, with areas 2 and 3 set to zero.
- Area 1: 12 x 10 = 120 sq ft
- Areas 2 and 3: 0
- Square yards: 120 / 9 = 13.3
- Square meters: 120 x 0.092903 = 11.1
The calculator shows "Total area: 120 sq ft." and "That is 13.3 sq yd or 11.1 square meters."
Example 2: an L-shaped room
Say the main part of a room is 12 x 10 ft and an extension off one side is 8 x 6 ft. Enter 12 and 10 as area 1, and 8 and 6 as area 2. The total is 120 + 48 = 168 sq ft, or 18.7 sq yd and 15.6 square meters. The key is to split the L so the two rectangles do not overlap; measure the extension only from where the main rectangle ends.
Example 3: feet and inches
A room that measures 12 ft 6 in by 10 ft 3 in becomes 12.5 x 10.25 = 128.125 sq ft. The calculator rounds the display to 128 sq ft.
Inches to decimal feet
| Inches | Feet | Inches | Feet |
|---|---|---|---|
| 1 in | 0.08 ft | 7 in | 0.58 ft |
| 2 in | 0.17 ft | 8 in | 0.67 ft |
| 3 in | 0.25 ft | 9 in | 0.75 ft |
| 4 in | 0.33 ft | 10 in | 0.83 ft |
| 5 in | 0.42 ft | 11 in | 0.92 ft |
| 6 in | 0.50 ft | 12 in | 1.00 ft |
Area formulas for other shapes
Not every space is a rectangle. These geometry formulas cover most of the rest. Work them out and add the result as its own line in your total (in the calculator, enter the area as a length with a width of 1).
| Shape | Formula | Example | Area |
|---|---|---|---|
| Rectangle or square | length x width | 12 x 10 ft | 120 sq ft |
| Right triangle | 1/2 x base x height | base 10 ft, height 6 ft | 30 sq ft |
| Trapezoid | (side a + side b) / 2 x height | parallel sides 10 and 6 ft, 8 ft apart | 64 sq ft |
| Circle | 3.1416 x radius x radius | 8 ft across (radius 4 ft) | About 50.3 sq ft |
| Half circle | 3.1416 x radius x radius / 2 | bay 8 ft across | About 25.1 sq ft |
For a room with a bay window or angled corner, measure the main rectangle, then treat the bay as a trapezoid or half circle and add it on.
Unit conversions
NIST defines these area relationships exactly, so you can convert with confidence:
| From | To | Multiply by |
|---|---|---|
| Square feet | Square yards | 1/9 (divide by 9) |
| Square yards | Square feet | 9 |
| Square feet | Square meters | 0.09290304 |
| Square meters | Square feet | About 10.764 |
| Acres | Square feet | 43,560 |
Room square footage vs. home square footage
Measuring a room for flooring is different from measuring a house for a listing or appraisal. Appraisals that follow Fannie Mae's guidelines use the ANSI Z765-2021 standard, and a few of its rules explain why the numbers rarely match:
- Exterior measurements. Sketches use exterior dimensions to the nearest tenth of a foot, so walls are included in the total. The final total is reported to the nearest whole square foot. Condos in multifamily buildings are the exception: Fannie Mae uses interior measurements for those.
- Ceiling height. Finished areas need a ceiling at least 7 ft high. Under a sloped ceiling, at least half of the room must reach 7 ft, and no counted part can be under 5 ft.
- Below-grade space is separate. Any level that is partly or fully below ground is reported as below-grade area, not added to the main total.
- Stairs and open-to-below areas. A staircase counts on the floor it descends from. Openings to the floor below, like a two-story foyer, do not count.
For a project, you want the interior, wall-to-wall measurement of the surface you are covering. For anything that involves the home's official size, ask your appraiser or agent which standard they use.
Measuring more than three areas
The calculator takes up to three rectangles at a time, which covers most single rooms. For a whole floor or an open plan with more pieces:
- Number every rectangle on your sketch so none gets skipped or counted twice.
- Run the calculator for the first three, write down the total, then clear the fields and run the next three.
- Add the subtotals by hand. If you are ordering flooring, apply the waste percentage to the grand total, not to each room, so rounding does not stack up.
- Keep the sketch with the measurements. It is the fastest way to double-check an order or answer an installer's question later.
The same method works outdoors. A patio, deck, or lawn with curves can be broken into rectangles plus a few half circles or triangles, then added up.
Using square footage for projects
Square footage is the starting point for most material estimates, but each material needs its own adjustment:
- Flooring and tile use the floor area plus a waste allowance for cuts. See the flooring calculator and tile calculator.
- Paint uses wall area, which is the perimeter times the height, not the floor area. The paint calculator handles that.
- Sod and lawn products use the yard's square footage; the sod calculator turns it into pallets.
Common mistakes to avoid
- Mixing inches and decimals. 10 ft 6 in is 10.5 ft. Writing 10.6 ft adds an extra 1.2 inches to every calculation.
- Overlapping rectangles. When you split an L-shaped room, make sure no part of the floor is counted twice.
- Forgetting closets. They often get the same flooring, so measure them as separate areas.
- Using floor area for walls. A 12 x 10 room has 120 sq ft of floor but about 350 sq ft of wall at 8 ft high, before doors and windows.
- Rounding down. If a measurement falls between marks, round up. A slightly high estimate costs a little extra material; a low one costs a second trip.
- Measuring over trim. Measure wall to wall at the floor, not from the face of the baseboard, when the new material will run under or up to the wall.
Frequently asked questions
How many square feet is a 12 x 12 room?
Multiply 12 by 12 to get 144 sq ft. That is 16 square yards, or about 13.4 square meters.
How do I calculate the square footage of an L-shaped room?
Split the L into two rectangles that do not overlap. Measure each one, multiply its length by its width, and add the two results. A 12 x 10 ft main area plus an 8 x 6 ft extension is 120 + 48 = 168 sq ft.
How do I convert square feet to square yards or square meters?
Divide square feet by 9 to get square yards, since a square yard is exactly 9 sq ft. Multiply square feet by 0.0929 to get square meters; NIST defines one square foot as exactly 0.09290304 square meters.
How many square feet are in an acre?
An acre is exactly 43,560 sq ft, according to NIST. A quarter acre is 10,890 sq ft.
How do I convert inches to feet for square footage?
Divide the inches by 12 and add them to the feet before you multiply. A wall that is 10 ft 6 in long is 10.5 ft, not 10.6 ft. Use the conversion table above for quick reference.
Why is my room total smaller than my home's listed square footage?
Appraisals that follow Fannie Mae's guidance and the ANSI Z765 standard measure a detached house from its exterior dimensions, so the total includes the walls themselves, hallways, and stairs (counted on the floor they descend from). Adding up interior room measurements leaves all of that out.