Square Footage Calculator
Add each room or area, pick its shape and enter the measurements in feet and inches (or meters and centimeters). You get each room's area and the grand total.
How it works
Rectangle = length × width. Triangle = base × height ÷ 2. Circle = π × (diameter ÷ 2)². Trapezoid = (side A + side B) ÷ 2 × height. Feet and inches are combined as feet + inches ÷ 12 (12 ft 6 in = 12.5 ft); meters and centimeters as meters + cm ÷ 100. The total is the sum of the rooms. 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.
- Feet and inches: a room 12 ft 6 in × 10 ft is 12.5 × 10 = 125 sq ft. Add a 6 × 8 ft closet as a second room (48 sq ft) for a total of 173 sq ft; with a 10% allowance, 190.3 sq ft (16.07 m² before the allowance).
- 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, add each part as its own room or area; the calculator adds them up.
- 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 content last updated 2026-10-19.