Square Footage Calculator

Area formulas by shape

Most rooms are rectangular, making the rectangle formula the most commonly used. For non-rectangular spaces, different formulas apply depending on the shape. Circles appear in features like round patios and ponds; triangles appear in attic floor plans and angled rooms; trapezoids appear in spaces with one pair of parallel walls of different lengths.

When working in metric units, the same formulas apply, but the result is in square metres rather than square feet. One square metre equals approximately 10.76 square feet. Converting between the two is useful when comparing international property listings or working with materials specified in different unit systems.

Practical uses of square footage

In real estate, gross floor area and net usable area are distinct measurements. Real estate listings in the US typically report total interior square footage, which may or may not include garage space, unfinished basement area, or covered outdoor space depending on local convention. When comparing properties, it is important to understand which definition of floor area is being used.

For flooring projects, you need the total area of the rooms being covered plus a waste allowance. Most flooring installers recommend ordering 10% extra for cuts and future repairs. For carpet, which comes in fixed-width rolls, the calculation must also account for directional patterns and seam placement, so the ordered quantity often exceeds the measured area by more than 10%.

Paint coverage depends on the wall area, not the floor area. A standard interior paint covers approximately 350–400 square feet per gallon on smooth surfaces. Textured surfaces, highly porous materials, and dark colours being replaced with lighter ones all reduce effective coverage and require additional coats.