Square Footage Calculator

Square footage is the currency of home projects: flooring and tile are sold by it, paint coverage is rated in it, rentals and real-estate listings are priced on it, and contractors quote by it. Getting the number right — before you buy materials or sign anything — starts with a tape measure and ends with this multiplication.

Measure in whatever unit is handy — feet, inches, yards, or meters — and the calculator returns the area in square feet with automatic conversions to square yards and square meters. The “identical areas” field totals several same-size spaces at once: four 10×12 bedrooms, two 12×10 rugs, a row of equal garden beds.

Buying flooring? Get the material count with waste allowance from the Flooring Calculator

Measure wall to wall at floor level along the two longest straight runs — length and width — then multiply:

For an irregular room, split it into rectangles, calculate each, and add them up — an L-shaped room is just two rectangles. Whole-house square footage is the sum of finished floor areas; listing conventions usually measure to the exterior walls and exclude garages, unfinished basements, and open porches, so a listed figure can differ from the sum of interior room measurements.

Quick answers for standard dimensions — every row is length × width:

So a 12×12 room is 144 square feet, a 20×20 space is 400 square feet, and a 30×40 building footprint is 1,200 square feet.

Not everything is a rectangle. The two other formulas you’ll actually need:

• Circle: Area = π × r², where r is half the width. A circular patio 12 ft across has r = 6 ft, so the area is π × 36 ≈ 113.1 sq ft.
• Triangle: Area = ½ × base × height. A triangular garden bed with a 10 ft base and 8 ft height is ½ × 10 × 8 = 40 sq ft.
• L-shapes and other compounds: slice the outline into rectangles (and triangles if needed), calculate each piece, and add.

Whatever the shape, convert the final area to square feet before pricing materials — coverage rates on flooring, paint, and mulch are all quoted per square foot in the US.

Cost = area × price per square foot. A 12×12 room (144 sq ft) at $4.50 per square foot of flooring is 144 × 4.50 = $648 in material. The same multiplication prices tile, carpet, refinishing, cleaning services, and rent quoted per square foot.

For materials that get cut — flooring planks, tile, wallpaper — add a waste allowance of roughly 5–10% before ordering, more for diagonal layouts or complex rooms. And note that paint is the exception to floor math: paint covers wall area, so measure each wall’s width × height and subtract windows and doors instead of using the floor’s square footage.