Square footage calculator.

To find square footage, multiply length by width in feet. A 12 ft by 15 ft room is 180 ft². For flooring, add 10% for waste: 198 ft², or 10 boxes that cover 20 ft² each. The square footage calculator also handles triangles, circles, trapezoids, wall area for paint, and lots that need square yards, square meters, or acres.

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Area of a rectangle, triangle, circle, or trapezoid

Pick the shape and the unit, then enter the measurements.

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Areacalterix
180 ft²
15 × 12 (ft) = 180 ft²
  • Square feet180 ft²
  • Square yards20 yd²
  • Square meters16.72 m²
  • Acres0.0041 acres

Area formulas by shape

ShapeFormulaExampleArea
Rectangle or squarelength × width15 × 12180 ft²
Trianglebase × height ÷ 210 × 6 ÷ 230 ft²
Circleπ × radius²π × 5²78.54 ft²
Trapezoid(long base + short base) × height ÷ 2(10 + 6) × 5 ÷ 240 ft²
Measurements in feet give an answer in square feet.

For odd shapes, split the outline into rectangles and triangles, find each area, and add. The lot tab does that sum and lets you subtract areas, like a pool or a cutout.

How much flooring or tile to buy

Room area = length × width − areas with no flooring
Flooring to buy = area × (1 + waste)
Boxes = flooring to buy ÷ ft² per box, rounded up
Example: 15 × 12 = 180 ft²; with 10% waste, 198 ft²; boxes of 20 ft² = 9.9, so 10 boxes.

Waste covers cuts along the edges, broken pieces, and a few spares for future repairs. Diagonal layouts, small rooms, and large tiles call for more, often 10% to 15%. The calculator starts at 10%, and you can edit the field.

For paint and wall tile, use the walls tab: perimeter times ceiling height, minus doors and windows. To work out the extra percent by hand, see the percentage calculator.

Area units and conversions

UnitEquals
1 square yard (yd²)9 ft²
1 acre43,560 ft²
1 square mile640 acres
1 square meter (m²)about 10.764 ft²
1 square footabout 0.0929 m²
Handy conversions for lots, rooms, and listings.
Linear feet are not square feet: 20 feet of baseboard is not 20 ft² of flooring. Always measure both dimensions. Square footage on a real estate listing can follow its own measuring rules, so measure yourself before you order materials.

To scale a measurement up or down, the proportion calculator helps. For quick one-off math, try the scientific calculator.

Frequently asked questions

How do you calculate square footage of a room?

Multiply the length by the width, both in feet. A 12 ft by 15 ft room is 180 ft². For L-shaped rooms, split the room into rectangles and add the areas.

How do you calculate square footage of a house?

Find the area of each room, then add them up. The lot tab adds several rectangles at once and subtracts cutouts. Listings may count walls, garages, or basements differently, so measure yourself for projects.

How many square feet are in an acre?

One acre is 43,560 square feet. A lot that measures 100 ft by 150 ft is 15,000 ft², which is about 0.34 acres.

How do you convert square meters to square feet?

Multiply square meters by 10.764. A 12 m² room is about 129.17 ft². Pick meters in the unit menu to convert as you calculate.

How do you calculate flooring with waste?

Multiply the room area by 1.10 for 10% waste. For 180 ft², buy 198 ft². Divide by the coverage of one box and round up to get the number of boxes.

How many square feet is a 10x12 room?

A 10 ft by 12 ft room is 120 ft². With 10% waste for flooring, buy about 132 ft².

Sources and method

Standard public-domain formulas. Every calculation is checked against independent numeric tests before it goes live.