How to calculate square footage
Square footage is just area, and for any rectangle area is length × width. Measure both sides in feet, multiply them, and you have the square footage of that space:
Square feet = length (ft) × width (ft)
A room 12 ft by 10 ft is 12 × 10 = 120 sq ft. For a whole house or project, measure each room or section as its own rectangle, work out each one, and add the results — which is exactly what the calculator above does when you fill in more than one area.
Measuring odd shapes
Few rooms are perfect rectangles, but almost any shape can be broken into rectangles:
- L-shaped rooms: split into two rectangles, calculate each, and add them (enter them as Area 1 and Area 2).
- Alcoves and bump-outs: treat each as its own small rectangle.
- Closets and hallways: measure and add them if you're flooring them too.
- Triangles: a right triangle is half of a rectangle — find ½ × base × height and add it on.
- Circles: area is π × radius² (the radius is half the diameter), so a 10 ft round patio is 3.14 × 5² ≈ 79 sq ft.
Converting units
| From | To square feet |
|---|---|
| Square inches | ÷ 144 |
| Square yards | × 9 |
| Square meters | × 10.764 |
| Acres | × 43,560 |
This calculator handles feet, inches, yards, and meters for you — pick your units at the top and it converts the total to square feet, square yards, and square meters.
Square footage for your project
Square footage is the starting point for almost every material estimate — once you have it, plug it into the right tool:
- Flooring & tile: the flooring, tile, and carpet calculators turn area into boxes, tiles, or yards.
- Paint: the paint calculator works from wall area (perimeter × height), not floor area.
- Lawns: the grass seed and mulch & soil calculators size seed and yards of material.
Why add a waste allowance?
If you're buying material to cover the area — flooring, tile, sod, or paint — add a waste allowance (often about 10%) so cuts, offcuts, and mistakes don't leave you short. Enter a percentage in the optional waste box and the total updates, and the cost is figured on the with-waste amount.
Tips for measuring accurately
- Use the right tool. A laser measure is fastest and most accurate for big rooms; a 25-ft tape is fine for smaller spaces. Measure at floor level, where the material actually goes.
- Measure twice. A small error in length or width gets multiplied across the whole area, so double-check each dimension before you trust it.
- Sketch as you go. Draw the space and write each measurement on it — that keeps L-shapes and bump-outs straight when you total them.
- Measure to the right edge. For flooring, measure wall-to-wall at the floor; for a deck or patio, measure the finished outside dimensions.
- Round up, not down. When a measurement falls between marks, round up — a slightly high estimate beats coming up short.