Square Footage Calculator

How this calculator works

Area is just length times width - but real rooms and lots are rarely one clean rectangle. The trick is to break the space into simple shapes, work out each one, and add them up. Anything that should not count - a stair void, a kitchen island, a pond the deck wraps around - is worked out the same way and subtracted:

rectangle = length × width
circle    = π × (diameter ÷ 2)²
triangle  = base × height ÷ 2
trapezoid = (side A + side B) ÷ 2 × gap
oval      = π ÷ 4 × length × width

total = (sum of added shapes) − (sum of subtracted shapes)

Each shape can repeat with a quantity, so five identical alcoves are one row. The subtracted shapes come off the added ones, and the net total is held at zero - an over-large cut-out can never push the area below nothing. The answer is shown in every common unit at once, so the same measurement works whether you think in square feet, square metres, square yards or acres.

Worked example

This example follows the unit system you pick in the calculator above.

An open living area: a 20 × 13 ft main room, plus a triangular bay (10 ft base, 6 ft deep), minus a round kitchen island 6 ft across:

1. Main room (rectangle): 20 × 13 = 260 sq ft.
2. Bay (triangle): 10 × 6 ÷ 2 = 30 sq ft.
3. Island (circle): π × (6 ÷ 2)² = 28.3 sq ft to subtract.
4. Net area: 260 + 30 − 28.3 = 261.7 sq ft.
5. That is also 29.1 sq yd and 24.3 m².

Shape formulas

Measure each piece, pick the matching shape, and the calculator applies the formula. The two main dimensions mean slightly different things per shape:

Area unit conversions

The calculator shows all of these together; this table is for quick mental checks.

Tips for measuring area

• Split, then add. Draw the space, divide it into rectangles and triangles with a few pencil lines, measure each, and total them. It beats trying to measure one awkward outline in a single go.
• Measure to the widest point for circles and ovals - the diameter, not the radius, and the full length and width of an oval, not half.
• Decide what to subtract before you start. For flooring you take out fixed islands and columns; for a lot area you usually do not. Measure cut-outs separately so you can use the figure either way.
• Use feet and inches as you read them. In imperial mode each measurement takes the feet and the inches in separate boxes, so a 12 ft 6 in wall is just 12 and 6 - no decimals to work out. Switch to metric for metres.
• Add a little for waste later. This tool gives the true area; the tile, paint, flooring and carpet calculators add the cutting and trim allowance on top, so do not pad the measurement here.

Turn the area into materials

This is the starting point - once you have the area, the material calculators take it from there:

• Tile calculator - boxes of tile and adhesive for a floor or wall area.
• Paint calculator - litres or gallons and how many coats for a given area.
• Flooring calculator - boards or planks, with the waste allowance, for a floor.
• Carpet calculator - broadloom by the roll width from the room area.

Measuring area where you are

In the United States, floor and room area is usually quoted in square feet (sq ft), and land in acres (1 acre = 43,560 sq ft). For homes, the finished living area (gross living area) is measured to the ANSI Z765 method, which the main mortgage buyers have required since 2022.

In roofing and siding a "square" means 100 sq ft, so a 2,000 sq ft roof is 20 squares.

For the local measuring rules, see the ANSI Z765 square-footage standard.