Measure the usable surface
Use inside dimensions for the surface that will actually receive material. Split an L-shaped room or irregular bed into simple rows instead of forcing one oversized rectangle.
Measure each shape, keep the math visible
Square footage calculator
Length × width in feet gives square feet. A 12 × 10 ft section plus a 6 × 4 ft section totals 144 sq ft before allowance. Enter your own non-overlapping areas below to see the total and unit conversions.
Rectangle, circle, triangle or known areaMultiple labeled zonesSquare feet, yards and metresNo login or usage limit
01 Measure each zone02 Choose the shape03 Review the total
Rectangle area = length × width · circle area = π × (diameter ÷ 2)² · triangle area = base × perpendicular height ÷ 2, or use three measured sides · square yards = square feet ÷ 9
Transparent area math
How this square footage calculator works
Choose US customary or metric units, then add one row for every measured space. A rectangle uses length × width, a circle uses its inside diameter, and a triangle uses either base and perpendicular height or three sides. A known-area row accepts the area you already measured. The page keeps each row visible and converts the total into square feet, square yards and square metres.
Use the right shape
A circle row uses diameter, not radius. For a triangle, choose base and perpendicular height or all three straight sides. If another tool already gave you a measured area, choose known area and keep that source number visible.
Keep allowance separate
Enter an allowance only when your project plan calls for one. The calculator shows measured and planning areas separately; it never hides a buffer inside the measured result.
US: dimensions in feet produce square feet directly. Metric: dimensions in metres produce square metres, then the page uses 1 m² = 10.763910416709722 sq ft and 1 sq yd = 9 sq ft for the displayed conversions.
The conversion follows the international foot, defined by NIST as exactly 0.3048 metre. Therefore 1 sq ft = 0.09290304 m². This worksheet does not determine official living area or property boundaries.
One acre equals 43,560 square feet. To convert square feet to acres, divide by 43,560; to convert acres to square feet, multiply by 43,560. For example, 0.25 acre × 43,560 = 10,890 sq ft. The acre output uses this exact ratio from NIST’s unit conversion table.
Three edges, no guessed height
Measuring a triangular garden bed
A sloping edge is not the perpendicular height. If you can measure the three straight edges of a flat triangle, select Triangle · three sides instead. The order of sides A, B and C does not matter.
With sides a, b and c, set s = (a + b + c) ÷ 2. The area is √[s × (s − a) × (s − b) × (s − c)], using Heron’s formula, documented by Wolfram MathWorld. Inputs in feet give square feet; metres give square metres.
Worked example, not a measured project: Sides of 3, 4 and 5 ft enclose 6 sq ft. Keep allowance at zero to copy the measured area. In the mulch calculator, choose known area, enter those 6 sq ft and your chosen depth. At an example depth of 3 inches, the volume is 1.5 cu ft; that depth is not a recommendation.
One area workflow, many jobs
From room measurements to material planning
Worked example, not a measured project: Two non-overlapping rectangles, 12 × 10 ft and 6 × 4 ft, give 120 + 24 = 144 sq ft. That is 16 sq yd or 13.38 m², rounded. Testing a 10% allowance changes the planning total to 158.4 sq ft; it does not change the measured 144 sq ft. The 10% is an example, not an installation recommendation.
For metric inputs, a 4 × 3 m rectangle plus a 2 × 1 m rectangle gives 14 m², or 150.69 sq ft, rounded. If a measurement includes inches, divide the inches by 12 first: 12 ft 6 in becomes 12.5 ft. For an obstacle, measure the remaining surface in separate rows or enter a net known area; this tool adds rows and does not subtract one automatically.
Start with a measured footprint, not a guessed coverage number. Once you have the square footage, use the result with the product label or project plan for the next calculation: mulch depth, soil volume, sod coverage, seed rate, paver layout or another material-specific worksheet.
Common questions
Square footage calculator FAQ
How do I calculate square feet?
For a rectangle, multiply length by width in feet. For a circle, use π × radius². Add separate rows when the space has more than one shape.
How do I measure square footage of a room?
Measure the usable inside length and width of each rectangular section, calculate each section, and add the rows. Use a circle, triangle or known-area row when that better matches the room.
Can I use this as an sq ft calculator?
Yes. Select US customary units for feet. The result includes square feet, square yards and square metres.
How do I convert square feet to square yards?
Divide square feet by 9. The page shows square yards beside the square-foot result.
Can I calculate square footage for more than one area?
Yes. Add one row per room, bed, patio section or other measured zone. Each row stays visible and the summary totals them.
Should I measure inside or outside dimensions?
Use the usable dimensions of the surface you are measuring. If walls, edging or framing take up space, measure the surface that the material will actually cover.
Does the calculator choose a waste allowance?
No. Enter the allowance you want to test. The measured area and planning area remain separate.
Do I need to log in or register?
No. This free square footage calculator runs in your browser without login, registration or a usage limit.
How do I enter feet and inches?
Convert inches to a decimal part of a foot first: divide inches by 12. Enter 12 feet 6 inches as 12.5 feet, not 12.6.
Does this calculator subtract obstacles?
No. Every row adds an area. Split the surface into non-overlapping sections, or calculate the net area separately and enter it as a known-area row. Do not add the obstacle as another row.
Can I find a triangular bed’s area from three sides?
Yes. Choose Triangle · three sides and enter all three straight-edge lengths in the same units. Heron’s formula finds the area without a height measurement. The longest side must be shorter than the other two combined. For curved or sloped surfaces, split the usable footprint into measured sections instead.
Connect the measurement
Use the area in the next calculator
For measured landscape materials, use the mulch calculator, soil calculator, grass seed calculator or fertilizer calculator. For a patio, compare the area with the paver calculator. For measured edges rather than surface coverage, add runs and subtract openings with the linear feet calculator.