Square Footage Calculator
Your estimate
- Acres
- 0.003 acres0.001 ha · 120 ft²
- Cost
- $360
Rooms, floors, lawns and lots — rectangles, L-shaped rooms, circles and triangles, with cost per square foot.
Updated 2026-10-20 · Based on: exact NIST unit definitions.
How to use the Square Footage Calculator
- Pick the shape of the area.
- Type the sizes — feet and inches both work (12 ft 6 in = 12.5 ft).
- Use Quantity for several identical rooms.
- Add a price per ft² to estimate flooring, sod or paint jobs.
Formula
Rectangle: length × width. L-shape: split it into two rectangles and add them.
Circle: π × (diameter ÷ 2)². Triangle: base × height ÷ 2.
1 yd² = 9 ft²; 1 m² = 10.764 ft²; 1 acre = 43,560 ft².
Worked example
With the values preset in the calculator above: (Rectangle)
- Length
- 12 ft
- Width
- 10 ft
- Quantity
- 1
- Square footage
- 120 ft² (13.33 yd²)
- Acres
- 0.003 acres (0.001 ha)
- Cost
- $360
How to calculate square footage of a room
Measure the longest length and width in feet. If a measurement has inches, divide the inches by 12 and add them (10 ft 9 in = 10.75 ft). Multiply length by width: a 12 × 10 ft room is 120 ft². For odd rooms, split the floor into rectangles, work each out and add them.
Square footage of common room sizes
| Length (ft) | Width (ft) | Square footage |
|---|---|---|
| 10 | 10 | 100 ft² |
| 12 | 12 | 144 ft² |
| 12 | 15 | 180 ft² |
| 20 | 20 | 400 ft² |
| 25 | 40 | 1,000 ft² |
| 50 | 100 | 5,000 ft² |
Related guides
Frequently asked questions
How do I calculate square feet from inches?
Multiply length × width in inches and divide by 144 (12 × 12). Or convert each side to feet first.
How many square feet is a 12 × 12 room?
144 ft² — that is 144 ft² (16 yd²) in other units too.
How many square feet in an acre?
43,560 ft², for example a lot 208.7 ft square or 66 × 660 ft.
More calculators
Estimates only — check quantities with your supplier and local building code before you order.