Square Footage Calculator

Calculate the area of a rectangle, square, triangle, or circle. Enter dimensions in feet, inches, yards, meters, or centimeters and get consistent conversions across common area units.

Shape

Dimension unit

Lengthft Enter a first dimension greater than zero

Widthft Enter a second dimension greater than zero

Identical areascount Multiplies the calculated shape area. Enter a whole number from 1 to 100,000

Calculation Results

Total area

—ft²

Calculated from the selected shape, dimensions, and quantity.

How to calculate square footage

Choose the shape

Use rectangle for four-sided spaces, square when all sides are equal, triangle for a base and perpendicular height, or circle when you know the diameter.

Choose the dimension unit

Both dimensions use the selected unit. The calculator converts at full precision before displaying square feet and metric results.

Enter measured dimensions

Measure along the same plane. For triangles, height must be perpendicular to the base. For circles, enter the full diameter rather than the radius.

Split irregular areas

Divide an irregular floor, wall, or lot into simple shapes, calculate each part separately, and add the resulting areas.

Area formulas and square-foot conversions

The geometric formula depends on the selected shape. Quantity multiplies the area after one shape is calculated. Linear dimensions are converted to feet before the square-foot result is produced.

Rectangle area = Length × Width

Square area = Side²

Triangle area = Base × Perpendicular height ÷ 2

Circle area = π × (Diameter ÷ 2)²

Total area = Area per shape × Quantity

Area conversion factors are squared length conversions. An acre contains 43,560 square feet, while one square foot equals exactly 0.09290304 square meter.

Common area conversions

Conversions shown from one square foot.

Target unit	1 ft² equals	Useful relationship
Square inches	144 in²	1 ft = 12 in
Square yards	0.111111 yd²	9 ft² = 1 yd²
Square meters	0.09290304 m²	Exact international-foot conversion
Acres	0.0000229568 ac	43,560 ft² = 1 acre
Hectares	0.000009290304 ha	10,000 m² = 1 hectare

Methodology, assumptions and sources

Every input dimension is converted to feet before the selected geometric formula is applied. Because area scales with the square of length, the conversion factor is applied to each dimension rather than to the final number as a linear conversion.

The circle calculation uses JavaScript’s full-precision value of π. Calculations retain precision until display, and no waste or material allowance is added.

Sources:

NIST Handbook 44, Appendix C (2026) — exact length and area conversion relationships, including square feet, square meters, acres, and hectares.

Last reviewed: August 2026. NIST does not endorse Efficienco.

Frequently asked questions

How do I calculate the square footage of a room?

For a rectangular room, multiply length by width. If the room is irregular, split it into rectangles or other simple shapes and add their areas.

How many square feet are in an acre?

One acre contains exactly 43,560 square feet.

Does a triangle use the sloped side or perpendicular height?

Use the perpendicular height from the base. A sloped side is not the triangle height unless it is perpendicular to the chosen base.

Can this estimate material quantity?

It calculates geometric area only. Material estimates should separately account for coverage, waste, cuts, overlaps, and packaging.