What is square footage?
Square footage (sq ft) is a measure of surface area: how many 1-foot by 1-foot squares would cover a floor, wall, lot or roof. It is the standard unit in the United States for room sizes, flooring, tile, carpet, paint, roofing and real estate listings.
This sq ft calculator works out the area of four common shapes in whatever unit you measured, then converts the answer to square feet, square yards, square meters and square inches so you can compare it with a product label or a quote.
How to calculate square feet by hand
- Measure each side in the same unit. Convert inches, yards, meters or centimeters to feet if you want the answer in square feet.
- Use the formula for the shape (see the formula box above).
- Multiply the area by the number of identical spaces.
- Add a waste percentage for materials.
If you measured in inches, remember that square inches divide by 144 to get square feet, not by 12.
Measuring tips for rooms that are not simple boxes
- L-shaped or irregular rooms: split the floor into rectangles, find each area, then add them up.
- Alcoves and closets: measure them as separate rectangles and add them if they will get the same flooring.
- Subtract what will not be covered: kitchen islands or built-in cabinets are often subtracted for flooring, but not for paint estimates unless they are large.
- Walls for paint: multiply wall width by height for each wall, add them up, then subtract doors and windows if they are large.
How much waste should you add?
Waste covers cuts around edges, damaged pieces and pattern matching. Typical rules of thumb are about 5% to 10% for straight plank or tile layouts, 10% to 15% for diagonal layouts, and more for large patterned tiles or rooms with many corners. Manufacturers and installers may recommend their own figure, so check the product instructions. Buying an extra box also helps if the style is discontinued later and you need repairs.
Unit conversion cheat sheet
| Unit | Equals in square feet |
|---|---|
| 1 square inch | 0.00694 sq ft (1/144) |
| 1 square yard | 9 sq ft |
| 1 square meter | 10.764 sq ft |
| 1 square centimeter | 0.00108 sq ft |
| 1 acre | 43,560 sq ft |
Carpet is often priced per square yard, while tile and hardwood are usually priced per square foot. The calculator shows both so you can compare prices fairly.
Common mistakes
- Mixing units, such as a length in feet and a width in inches.
- Measuring the wrong thing for a circle: use the diameter (across), or half of it for the radius, but never mix them up.
- Forgetting waste, which leaves you short on materials.
- Using the square footage of a house listing for flooring. Listings usually include walls, closets and sometimes stairs.
Related measurements
For lumber, use a board foot calculator, which measures volume rather than area. For concrete, gravel or mulch you need cubic measurements: multiply the area in square feet by the depth in feet to get cubic feet, then divide by 27 for cubic yards.