Measure calculator
Square Footage Calculator
Measure the shape, apply the matching area formula, and add only the allowance your material needs. The calculator reports both the measured area and the adjusted purchasing area.
Planning estimate, not a contractor quote. Review the assumptions and replace presets with local prices when available.
Method
How this calculator works
Square footage is the starting point for flooring, paint, patios, driveways, roofing, and dozens of other projects. Rectangles are simple, but circles, triangles, and tapered areas need different formulas. Calculate each section separately when a room or yard is irregular, then add the sections together.
Rectangle: length × width. Circle: π × (diameter ÷ 2)². Triangle: base × height ÷ 2. Trapezoid: (parallel side A + parallel side B) × perpendicular height ÷ 2. Multiply by quantity, then apply the optional allowance.
Worked example
A realistic starting point
A 12 ft by 10 ft rectangle is 120 ft². With no extra allowance, that is also 13.33 yd² or 11.15 m². A 10 ft diameter circle is 78.54 ft².
What changes the answer
Factors worth checking
Split irregular spaces
Break L-shaped rooms and curved yards into simple sections. Add the section areas instead of estimating one oversized rectangle.
Use finished dimensions
Measure the surface that will actually receive material. Openings, cabinets, borders, and built-ins may change the net area.
Match waste to material
Tile patterns, wood grading, paver cuts, and sheet-goods layouts need different allowances. Zero is appropriate when you only need the geometric area.
Keep units consistent
Do not mix inches and feet inside one formula. Convert first, then calculate.
Common questions
Square footage FAQ
How many square feet are in a square yard?
One square yard equals 9 square feet because it is 3 feet by 3 feet.
Should I subtract doors and windows?
For exact finish quantities, subtract large untreated openings. For paint, many estimators leave smaller openings in the total to provide a practical allowance.
What waste percentage should I use?
It depends on the material and layout. Straight installations often use less; diagonal patterns, complex cuts, and natural variation generally need more.
Can I add several rooms?
Yes. Calculate each room as a separate shape, or use quantity when the dimensions are identical, then add the adjusted totals.
Evidence
Sources & review
- NIST Handbook 44 — Units of MeasureUS customary and metric unit references.
Published by Calcstead. Report a correction.
Method and source links reviewed September 4, 2026. Price presets are editable planning inputs and should be replaced with current local information.