Square Footage Calculator
Calculate the square footage of a room or area, with support for combining multiple rectangles. Enter length and width to get area in square feet and square meters. The starting point for flooring, paint, tiling, and most material estimates.
Shape Reference
How the Formula Works
Rectangle area
Area (ft²) = Length (ft) × Width (ft) Multiply the two perpendicular dimensions. For rooms, measure wall-to-wall length and wall-to-wall width at floor level. Add a 5–10% waste factor for flooring or tiling to account for cuts and off-cuts.
Square area
Area (ft²) = Side (ft) × Side (ft) = Side² A square is a special case of a rectangle where all four sides are equal. Square a single side measurement to get the area. Common for patios, tiles, and symmetrical rooms.
Triangle area
Area (ft²) = ½ × Base (ft) × Height (ft) Height is the perpendicular distance from the base to the opposite apex — not the slant height. Perimeter uses an isosceles approximation: P = Base + 2 × √((Base/2)² + Height²). For non-isosceles triangles, measure all three sides directly.
Circle area
Area (ft²) = π × Radius (ft)² Enter the radius (half the diameter). Circumference = 2 × π × Radius. Use this for circular patios, pools, round rooms, or any curved footprint.
Unit conversions
Area (m²) = Area (ft²) × 0.092903 | Acres = Area (ft²) ÷ 43,560 | Hectares = Area (m²) ÷ 10,000 One square foot equals 0.092903 square metres. One acre is 43,560 square feet. One hectare is 10,000 square metres (≈ 2.471 acres). These conversions are applied automatically to every result.
Frequently Asked Questions
Square footage is a measurement of area expressed in square feet (ft²). One square foot is the area of a square with sides 1 foot long. It is the standard area unit used in the United States for real estate listings, flooring, roofing, paint coverage, and construction material estimates. To find the square footage of a rectangle, multiply its length by its width.
Measure the room's length and width at floor level using a tape measure. Multiply the two numbers: Area = Length × Width. For example, a 12 ft × 10 ft room is 120 ft². For L-shaped or irregular rooms, break the space into rectangles, calculate each one separately, then add the totals together.
Calculate the room's square footage, then add a waste factor before ordering materials. For hardwood or laminate, add 7–10% for cuts and alignment. For tile set on the diagonal, add 10–15%. For carpet, add 5–10% for seam placement. Always buy slightly more than you need — matching dye lots later can be difficult.
A standard gallon of interior paint covers 350–400 ft² per coat. Calculate your wall area (perimeter × ceiling height, minus windows and doors), then divide by 350 for a conservative estimate. Add 10–15% for a second coat or porous surfaces like new drywall. Ceilings and trim require separate calculations.
Measure the footprint of the house (length × width), then multiply by a pitch factor for the slope. A flat roof uses a 1.0 factor; a 4/12 pitch uses about 1.054; a 6/12 pitch uses about 1.118; a 12/12 pitch uses about 1.414. For example, a 1,200 ft² footprint on a 6/12 pitch roof has approximately 1,341 ft² of actual roof surface. Add 10–15% for waste and ridge/hip cuts.
One acre equals exactly 43,560 square feet. It is roughly the area of a football field (without the end zones). To convert square feet to acres, divide by 43,560. For example, a 100 ft × 200 ft lot is 20,000 ft² = 0.459 acres. This calculator shows acres automatically alongside square footage.
One hectare equals 10,000 square metres or approximately 107,639 square feet (about 2.471 acres). Hectares are the standard land area unit in most countries outside the United States. This calculator converts to hectares automatically from any shape input.
Use imperial (feet and inches) for US residential construction, real estate, and retail material purchasing — most US product sizes and coverage rates are expressed in ft². Switch to metric for international projects, scientific calculations, or when materials are priced per m². This calculator supports both unit systems and converts results automatically between ft², m², acres, and hectares.
Perimeter is the total distance around the outside of a shape. Rectangle: P = 2 × (Length + Width). Square: P = 4 × Side. Circle (circumference): C = 2 × π × Radius. Triangle (isosceles): P = Base + 2 × √((Base/2)² + Height²). Perimeter is useful for fencing, baseboard trim, edging, and any material sold by the linear foot.
Contractors use square footage as the primary unit for material take-offs and labor estimates. Framing labor is often quoted per ft² of floor area; roofing and siding are quoted per "square" (100 ft²); concrete flatwork is priced per ft². Accurate area measurements reduce material waste and prevent costly shortages. Always add a project-specific waste allowance (5–15%) on top of the calculated area before purchasing materials.