How to use this square footage calculator
- Choose Measurements in: Feet and inches, Decimal feet, or Meters and cm. Typed lengths convert when you switch.
- In Area 1, pick a Shape and type each dimension. The diagram and area update as you type.
- Set Count this area as to Add for rooms or Subtract for islands, stairwells and hearths.
- Use Add another area for each extra room, up to 30.
- Under Materials and cost, choose a waste percent, pick the unit in Prices are per, and enter a price. Switching units never changes a typed price.
How to measure a room
Measure wall to wall at floor level along the longest and widest points, to the nearest inch, and measure twice: an inch off across a 12 ft wall is about 1 sq ft. Enter alcoves and closets as separate areas.
Formulas for each shape
- Rectangle or square:
length x width. The rectangle area calculator adds perimeter and diagonal. - L-shape: two rectangles added, or overall length x width minus the missing corner.
- Circle:
3.14159 x radius x radius. A half circle is half of that, a quarter circle one quarter. - Triangle:
1/2 x base x height, or Heron's formula for three sides:square root of s x (s - a) x (s - b) x (s - c), where s is half the perimeter. - Trapezoid:
1/2 x (parallel side A + parallel side B) x height.
Worked example with the default inputs
The page opens with a living room 12 ft 3 in by 10 ft 6 in, which is 12.25 ft x 10.5 ft = 128.625, shown as 128.63 sq ft. Divide by 9 for 14.29 sq yd, or multiply by 0.09290304 for 11.95 sq m. With the default 10% waste you order 141.49 sq ft (15.72 sq yd), and at $4.00 per sq ft the material cost is $565.95.
Square yards and carpet
Carpet is sold by the square yard, so divide square feet by 9: 144 sq ft is 16 sq yd. Use the carpet calculator for roll widths and seams, and the tile calculator for tiles.
Measuring a whole house
The usual US guide is ANSI Z765 for single-family houses: finished, heated, above-grade space measured to the outside of the exterior walls. Garages and unfinished areas are left out, and basements, even finished ones, are reported separately as below-grade area. Summing interior rooms comes out lower. Not an appraisal.
Uses for cost per square foot
Multiply area by a price per sq ft to budget flooring, carpet, tile or sod, or divide a home's price by its finished square feet.
Limits and edge cases
Flat areas only, each measurement above 0 and under 1,000,000 ft. A card with a missing or invalid number is left out and flagged. If Subtract areas equal or exceed Add areas, there is no total.
Square footage calculator FAQ
How do I calculate the square footage of a room?
Multiply length by width in feet: 12 ft 3 in by 10 ft 6 in is 12.25 x 10.5 = 128.63 square feet. Split other shapes into rectangles, triangles or circles and add them.
How do I find the square footage of an L-shaped room?
Add two rectangles, or take the overall length times width and subtract the missing corner. A 20 ft by 15 ft room missing an 8 ft by 5 ft corner is 20 x 15 minus 8 x 5, which is 260 square feet.
How many square feet is a 12x12 room?
A 12 ft by 12 ft room is 144 square feet, which is 16 square yards or about 13.38 square meters.
How do I convert square feet to square yards?
Divide by 9, because a square yard is 3 ft by 3 ft. For example, 144 square feet is 16 square yards.
How much extra flooring should I buy?
Most people add 5 to 10 percent for a simple straight layout and 10 to 15 percent for tile, diagonals or many corners. For 128.63 square feet, 10 percent extra means ordering 141.49 square feet.
Sources: Home Innovation Research Labs, ANSI Z765; NIST, 1 ft = 0.3048 m exactly; MathWorld, Heron's formula. Estimates only.