Square Footage Calculator
Find the square footage of rooms and shapes (rectangles, circles, triangles and more), add several areas together, and estimate the cost at a price per square foot or metre.
Change the values and press Calculate to work out your own figures.
Rectangle (optional border)
Length × width, for rooms and most floors. Add a border width to measure only a path or frame around the inside edge.
Show the working
- Area = length × width = 144 sq ft
Square (optional border)
Side × side. Add a border width to measure only the strip around the inside edge.
Show the working
- Area = side² = 225 sq ft
Circle or ring
Enter the diameter (the distance across). Add a border width to measure a ring.
Show the working
- Area = π × D² ÷ 4 = 78.5398163397 sq ft
- × 2 = 157.079632679 sq ft
Triangle from three sides
Enter all three sides when you can’t measure the height.
Show the working
- Area = Heron: √(s(s−a)(s−b)(s−c)), s = (a+b+c)/2 = 6 sq ft
Triangle from base and height
Base × height ÷ 2, when you know the height at a right angle to the base.
Show the working
- Area = base × height ÷ 2 = 40 sq ft
Trapezoid
Two parallel sides and the distance between them.
Show the working
- Area = (base 1 + base 2) × height ÷ 2 = 15 sq ft
Circle sector
A slice of a circle: enter the radius and the angle of the slice.
Show the working
- Area = angle (radians) × radius² ÷ 2 = 78.5398163397 sq ft
Parallelogram
Base × height, where height is measured at a right angle to the base.
Show the working
- Area = base × height = 600 sq ft
Several rooms or areas
Add each room or area with its own shape, and get the combined total and cost.
Show the working
- Area 1 (rectangle): 184 sq ft
- Area 2 (circle × 2): 157.079632679 sq ft
- Area 3 (triangle sides): 6 sq ft
- Cost = 347.079632679 sq ft × $2.5 = $867.70
How to measure a room
- Measure the length and width of the floor along the walls, at floor level.
- For an L-shaped or irregular room, split it into rectangles (and triangles or circles where needed) and add each one as its own area.
- Enter each measurement in the unit you used. You can type tape-measure readings such as 12' 6" or 12 1/2 directly.
- Use the quantity box for identical areas, such as three bedrooms of the same size.
Square footage is the area of a floor plan, measured flat. For sloped surfaces such as roofs, or for walls, use the dedicated construction tools, which account for pitch, openings and waste.
Area formulas
Rectangle: length × width Square: side × side Circle: π × diameter² ÷ 4 Triangle: base × height ÷ 2 Triangle from three sides: √(s(s − a)(s − b)(s − c)), where s = (a + b + c) ÷ 2 Trapezoid: (side 1 + side 2) × height ÷ 2 Circle slice: angle in radians × radius² ÷ 2
For example, a 12 ft 6 in by 10 ft room is 12.5 × 10 = 125 square feet. At $3.50 per square foot, flooring for it would cost about $437.50 before waste, underlay and labour.
Borders and rings
The border option measures only a strip around the inside edge of a shape, such as a tiled border or a path inside a garden bed. A 30 × 20 ft area with a 2 ft border has 600 − (26 × 16) = 184 square feet of border. For a circle, the border gives the area of a ring.
Converting square feet
Every result is also shown in square inches, square yards, acres, square metres, square centimetres and square kilometres. The factors are exact: 1 square foot is 0.09290304 square metres, 1 square yard is 9 square feet, and 1 acre is 43,560 square feet.
Questions
How do I calculate square feet from inches?
Multiply length by width in inches, then divide by 144, because a square foot is 12 × 12 = 144 square inches. Or just choose inches as the unit and the calculator converts for you.
Should I add extra for waste?
This calculator gives the exact area. When buying flooring or tiles, most people add 5–10% for cuts and breakage; the flooring and tile calculators include a waste allowance.
How many square feet are in a square metre?
About 10.7639. One square metre is exactly 1 ÷ 0.09290304 square feet.
Sources
- OpenStax Prealgebra 2e, 9.4 Use Properties of Rectangles, Triangles, and Trapezoids
- OpenStax Prealgebra 2e, 9.5 Solve Geometry Applications: Circles and Irregular Figures
- OpenStax Precalculus 2e, 8.2 Non-right Triangles: Law of Cosines
- OpenStax Algebra and Trigonometry 2e, 7.1 Angles
- NIST SP 811 Appendix B.9, conversion factors by kind (area, length)
- NIST Handbook 44 (2026), Appendix C: General Tables of Units of Measurement
- NIST, U.S. Survey Foot
Limitations
- Dimensions are treated as horizontal plan measurements; sloped or irregular surfaces must be split into supported shapes.
- Border width is measured inward from the outer edge (a frame or path inside the outline); an outward border must be entered as a larger outer shape.
- Cost is a simple area × unit price estimate in USD; taxes, waste and labour are not included.
- Wall/ceiling paint coverage, flooring waste and material ordering are handled by separate construction tools.