Square Footage Calculator
Pick a shape and enter its measurements to get the area in square feet, square yards and square meters.
How it works
Rectangle = length × width. Triangle = base × height ÷ 2. Circle = π × (diameter ÷ 2)². Trapezoid = (side A + side B) ÷ 2 × height. Square yards = square feet ÷ 9. Square meters = square feet × 0.09290304 (from 1 ft = 0.3048 m exactly, NIST).
Worked examples
- A 12 × 15 ft room is 180 sq ft = 20 sq yd = 16.72 m². A 5 × 4 m area entered in metric is 20 m² (215.3 sq ft).
- L-shaped room: split it into a 12 × 15 ft rectangle (180 sq ft) and a 6 × 8 ft rectangle (48 sq ft). Total 228 sq ft = 25.3 sq yd = 21.2 m².
- Round patio 10 ft across: π × 5² = 78.5 sq ft (7.30 m²). Triangle with a 10 ft base and 6 ft height: 10 × 6 ÷ 2 = 30 sq ft.
How to measure
- Use a tape measure or laser measure and write down each wall length, to the nearest inch or centimeter.
- Measure wall to wall at floor level. Ignore baseboards; for flooring, measure into doorways and closets that get the same floor.
- Sketch the room. Split L-shapes and alcoves into rectangles and triangles and measure each one.
- Convert feet and inches to decimal feet before you enter them: 12 ft 6 in is 12.5 ft (6 ÷ 12 = 0.5).
Common mistakes
- Reading 12 ft 6 in as 12.6 ft. Inches are twelfths of a foot, so it is 12.5 ft.
- Using a slanted side as the height of a triangle or trapezoid. Height is measured at a right angle to the base.
- Adding the waste allowance twice, here and again in a flooring or tile calculator. Add it once.
- Using square feet where square yards are wanted (carpet and some sod are sold by the square yard). Divide sq ft by 9.
- Forgetting closets, bump-outs or the area under appliances that will also get the new floor.
Assumptions
- Measurements are straight-line and the surface is flat. For L-shaped or irregular rooms, split them into rectangles and add the results.
- Triangle height is measured at a right angle to the base.
- Nothing is subtracted for cabinets, islands or columns; subtract those areas yourself if needed.
- The waste allowance is an editable JobsiteCalc default, not an industry standard. Ask your supplier what extra they suggest for your job.
Frequently asked questions
How do I calculate square footage of a room?
Multiply the length by the width in feet. A 12 × 15 ft room is 180 square feet. For an L-shaped room, split it into two rectangles and add them.
How many square feet are in a square yard?
Nine, because a square yard is 3 ft × 3 ft.
How do I convert square feet to square meters?
Multiply by 0.09290304. NIST defines 1 foot as exactly 0.3048 meters, and 0.3048² = 0.09290304.
Related calculators
- Flooring calculator – turns floor area into cartons with a waste allowance
- Tile calculator – tiles and boxes, with grout joints
- Paint calculator – wall area and gallons for a room
- Drywall calculator – sheets for walls and ceilings
- Sod and grass seed calculator – for lawn areas
Sources
Formulas and reference values are from these sources. Page last reviewed 2026-10-19.