How it works
- Square feet = length × width in feet, for each rectangle.
- A triangle is half its base × height.
- A circle is π × radius².
- Inches are divided by 12 first.
Square yards = square feet ÷ 9. Square meters = square feet × 0.09290304, from the international foot. Acres = square feet ÷ 43,560.
Worked example
A 12 × 12 ft room: 12 × 12 = 144 sq ft, which is 16 sq yd, 13.38 m² or 0.0033 acres. For an L-shaped room, add a second rectangle with “+ Add another area”.
Tips and common mistakes
- Measure wall to wall at floor level.
- Split odd shapes into rectangles and triangles.
- Round measurements up to the next inch.
Questions about this calculator
How do I calculate sq ft?
Multiply length by width in feet. For a room 12 ft by 14 ft, that is 168 sq ft.
How many sq ft is in a 12x12 room?
144 sq ft.
How many sq ft is 30x40?
1,200 sq ft.
What is the sq ft of a 20x20 room?
400 sq ft.
Sources
Values marked with a link come from the linked source, which opens in a new tab. Unit conversions and our own defaults are listed separately. Every value the site uses is in the methodology source register.
Where the numbers come from 2
- Square feet per acre
- 43560 sq ft/acre
- NIST, revised unit conversion factors (international foot, from 2023): "43,560 ft2 = 10 ch2 = 160 rd2" (opens in a new tab)nist.gov
- Meters per international foot
- 0.3048 m/ft
- NIST, international foot conversion (opens in a new tab)nist.gov
Unit conversions and our defaults8
- Feet per yard
- 3 ft/yd
- Unit definition: one yard contains three feet
- Inches per foot
- 12 in/ft
- Unit definition: one foot contains twelve inches
- Centimeters per meter
- 100 cm/m
- Metric prefix definition: centi is one hundredth
- Circle constant π
- ≈ 3.14159 unitless
- Circle geometry, as specified in the owner brief
- Square footage calculator starting area
- 12, 12 ft length, ft width
- Wave 2 pack worked example; editable starting measurements
- Square footage unit-check threshold
- 10000 ft
- Owner specified unit-check warning, not a size limit
- Rooms that can be added in one estimate
- 8 rooms
- Build choice: keeps the form manageable; run the tool again for more rooms
- Volume and weight display precision
- 2 decimal places
- Owner specification: display volume and tons to two decimals
By Taimoor Zayad, DAE in Civil Engineering, three years as a site supervisor.Last updated How we calculate