Area Calculator

For a rectangular area, multiply length by width. A room 12 ft × 10 ft is 120 sq ft (a 3.7 m × 3.0 m room is about 11.1 m²). Pick the Rectangle shape, type the two sides in whatever unit you measured — feet, inches, metres or millimetres — and the square footage (or m²) is worked out for you, along with the perimeter.

Split it into simple shapes — rectangles and triangles — work out each one, and add the results together. Most rooms break down into two or three rectangles; a bay or a corner is usually a triangle or a sector. Do each piece here and press “Add to total”: the calculator keeps a running total, lets you set a quantity for identical pieces, and adds an optional waste allowance — so you get the combined square footage in one figure.

Area = π × radius². Choose the Circle shape and enter either the diameter or the radius (there is a toggle). A circle 10 ft across (5 ft radius) is about 78.5 sq ft; a 3 m diameter (1.5 m radius) is about 7.1 m². The calculator also returns the circumference.

Area = ½ × base × height, where the height is measured at a right angle to the base — not along a sloping side. A triangle with a 6 ft base and 4 ft height is 12 sq ft. If you only know the three side lengths, switch to “Three sides” and the calculator uses Heron’s formula and also gives the perimeter.

Area = ½ × (a + b) × height, where a and b are the two parallel sides and the height is the perpendicular distance between them. Parallel sides of 10 ft and 6 ft, 4 ft apart, give ½ × 16 × 4 = 32 sq ft.

Yes. “Rectangle with border” and “Triangle with border” give the area of a uniform-width frame or path running around the inside edge (plus the total and inner areas), which is what you need for edging, skirting or a border planting. “Ring / annulus” gives the area between an outer and inner circle — a hollow column, pipe wall or circular path.