How to use the square feet calculator
- Choose the unit you measured in.
- For each part of the space, choose its shape and enter its dimensions: length and width for a rectangle, base and height for a triangle, or diameter for a circle.
- Add more areas for L-shaped or irregular spaces. Tick Subtract this area for cut-outs such as a fireplace hearth or kitchen island.
- Optionally enter a price per square foot to estimate cost.
How the calculation works
Area is the flat surface inside a shape, measured in square units. A rectangle’s area is length × width; a triangle is half of the rectangle that encloses it (½ × base × height, where the height is measured at a right angle to the base); a circle is π × radius².
The calculator converts each dimension from the unit you chose, works out every shape’s area, then adds the shapes and subtracts any marked as cut-outs. Splitting a space this way lets you measure almost any floor plan: an L-shaped room is two rectangles, and a bay window is a rectangle plus a triangle or half-circle.
The total is reported in square feet (1 sq ft = 0.09290304 m² exactly), square meters, square yards (9 sq ft) and acres (43,560 sq ft). Remember that 1 square foot is 144 square inches, not 12, because squaring the units squares the conversion factor.
Formula
Worked examples
A 14 × 12 ft room with a 6 × 4 ft triangular bay
Rectangle: 14 × 12 = 168 sq ft. Triangle: ½ × 6 × 4 = 12 sq ft. Total = 180 sq ft (16.72 m²).
Converting from inches
A 96 × 60 in countertop = 5,760 sq in ÷ 144 = 40 sq ft.
Assumptions and limitations
- Assumes flat surfaces. For roofs, multiply the plan area by the roof slope factor (see the rafter calculator).
- Measure to the nearest inch or centimeter; small errors grow when multiplied.
- When buying materials, add a waste allowance appropriate for the product.
Frequently asked questions
How do I calculate square feet?
Multiply length by width in feet. If you measured in inches, multiply and then divide by 144.
How many square feet are in a square meter?
About 10.764 sq ft. One square foot is exactly 0.09290304 m².
How do I find the square footage of an L-shaped room?
Split it into two rectangles, calculate each, and add them. Enter each rectangle as its own area above.