CalcNest

Square Footage Calculator

Measure a room, floor or yard in feet and inches and get its area in square feet — plus square yards, square meters and the cost with waste.

By Rachel Okafor, CPA · Last reviewed

Length
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Width
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Section 1 length
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Section 1 width
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Section 2 length
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Section 2 width
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Diameter
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Base
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Height
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Top side
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Bottom side
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Height
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Result

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  • Square yards
  • Square meters
  • Acres
  • To buy, with waste
  • Cost

Measuring area in square feet

Square footage is what you buy flooring, sod, paint coverage, roofing and sealant by, and what rents and home prices are compared on. Any floor plan can be broken into simple shapes — rectangles, triangles, circles — measured separately and added. Measure to the nearest inch, convert inches to decimal feet, and only round the final answer.

The formulas

feet = ft + in ÷ 12 Rectangle: L × W L-shape: L₁ × W₁ + L₂ × W₂ Circle: π × (D ÷ 2)² Triangle: ½ × base × height Trapezoid: ½ × (top + bottom) × height 1 yd² = 9 ft² 1 m² = 10.7639 ft² 1 acre = 43,560 ft²

Worked example

A 12 ft × 15 ft bedroom = 180 ft² = 20 yd² = 16.72 m². For laminate with 10% waste, buy 198 ft²; at $3.50/ft² that is $693.00.

An L-shaped living room of 12 × 15 ft plus a 6 × 8 ft nook = 180 + 48 = 228 ft². A circular patio 10 ft across = π × 5² = 78.54 ft².

Notes

  • For walls, measure each wall's width × height and subtract doors (about 21 ft²) and windows.
  • Results are rounded to 2 decimals for display.

Sources: NIST, Handbook 44, Appendix C (area units); ANSI Z765-2021, Single-Family Residential Buildings — Square Footage Method for Calculating.

Frequently asked questions

How do I calculate square footage of a room?

Measure the length and width in feet and multiply. A 12 ft × 15 ft bedroom is 180 square feet. If a measurement has inches, convert them to a fraction of a foot first: 12 ft 6 in = 12.5 ft. For an L-shaped room, split it into two rectangles and add their areas.

How much extra flooring should I buy?

Flooring installers commonly add 5–10% for cuts and waste on straight layouts, and 15% or more for diagonal or herringbone patterns and rooms with many corners. Set the waste percentage and the calculator adds it to the amount to buy and the cost.

How do I convert square feet to square yards or square meters?

Divide square feet by 9 for square yards (carpet is often priced per square yard): 180 ft² = 20 yd². Multiply by 0.09290304 for square meters: 180 ft² = 16.72 m². An acre is 43,560 ft².

Does square footage of a house include the garage?

For listings and appraisals in the U.S., finished above-grade living area is measured from the exterior walls under ANSI Z765; garages, unfinished basements and open porches are reported separately. This calculator measures any flat area you enter — use interior dimensions for flooring and paint.