How to calculate square footage
Square footage is just length × width. A 12 × 15 ft room is 180 square feet. The only real trick is odd shapes — break them into rectangles and add. Here's how to measure any space, handle the awkward bits, and convert to yards or meters.
The basic formula
For any rectangle, measure both sides in feet and multiply:
Square footage = length (ft) × width (ft)
If you measured in inches, divide each measurement by 12 first (or measure in feet and tenths — 12 ft 6 in is 12.5 ft). Multiply, and the answer is in square feet.
Odd shapes: split and add
Most rooms aren't perfect rectangles. The fix is always the same — divide the space into shapes you can measure, then add the pieces:
- L-shapes and alcoves: draw a line to split the floor into two rectangles, calculate each, and sum them.
- Triangles: area = ½ × base × height. Handy for angled bay windows and corner cut-offs.
- Circles and curves: area = π × radius² (radius is half the width). A round patio 10 ft across is 3.14 × 5² ≈ 79 sq ft.
A worked example
Say you have an L-shaped living room. Split it into a main rectangle and the extension:
- Main area: 12 ft × 16 ft = 192 sq ft
- Extension: 6 ft × 8 ft = 48 sq ft
- Total: 192 + 48 = 240 sq ft
That total is what you'd take to a flooring or paint estimate — then add waste on top.
Multiple rooms or odd shapes?
The square footage calculator adds up several rooms at once and converts to square yards and meters — with an optional waste allowance for materials.
Open the Square Footage CalculatorConverting to yards and meters
- Square yards (carpet, concrete): square feet ÷ 9. So 180 sq ft = 20 sq yd.
- Square meters (metric products): square feet × 0.0929. So 180 sq ft ≈ 16.7 sq m.
Square footage of common rooms
| Room size | Square feet | Square yards |
|---|---|---|
| 10 × 10 ft | 100 sq ft | 11.1 sq yd |
| 12 × 12 ft | 144 sq ft | 16.0 sq yd |
| 12 × 15 ft | 180 sq ft | 20.0 sq yd |
| 15 × 20 ft | 300 sq ft | 33.3 sq yd |
| 20 × 20 ft | 400 sq ft | 44.4 sq yd |
Don't forget waste
Square footage tells you the area — but you almost always buy more than that. Flooring and tile typically add about 10% for cuts and offcuts (15% for diagonal or herringbone layouts), and paint is figured on wall area, not floor area. Work out the clean square footage first, then add the waste for whatever you're buying.