Square Footage Calculator
Find the area of a room, a whole floor or an awkward L-shaped space in seconds. Add as many rectangles, triangles, circles and trapezoids as you need, subtract cut-outs, and get the answer in square feet, square metres and square yards at the same time. It is ideal for flooring, carpet, paint planning and comparing property sizes.
Square footage calculator
Add one row per section. Imperial accepts feet and inches such as 12' 6" or 12 6. Use “Subtract” for cut-outs such as a chimney breast or kitchen island.
How to use the square footage calculator
- Split the space into simple shapes. Sketch the room and divide it into rectangles, triangles, circles or trapezoids. An L-shaped room is two rectangles, or one big rectangle minus a small one.
- Enter the first shape. Choose the shape and type its dimensions. In imperial you can type feet and inches such as 12' 6" or 12 6; in metric use metres.
- Add or subtract more sections. Click Add section for each extra piece. Set Mode to Subtract for things you do not want to count, such as a fireplace hearth or fitted kitchen island.
- Add waste and price if needed. For flooring, add a waste allowance. Enter a price per square foot or per square metre to get a rough material cost.
- Read the totals. The total appears in sq ft, m² and sq yd, along with the area of each section so you can check your working.
The formula explained
Area is always two lengths multiplied together, so the unit is “square something”. The calculator converts every dimension to metres internally, works out each shape, adds or subtracts them, and then converts the total back.
Rectangle: A = Length × Width
Triangle: A = ½ × Base × Height
Circle: A = π × (Diameter ÷ 2)²
Trapezoid: A = ½ × (Side a + Side b) × Height
Total = Σ added shapes − Σ subtracted shapes
For a triangle, the height must be measured at right angles to the base, not along the sloping side. For a trapezoid (a shape with two parallel sides, such as a bay or a tapering corridor), sides a and b are the two parallel sides and the height is the distance between them.
Unit conversions use exact factors. One foot is 0.3048 m, so one square foot is 0.3048² = 0.09290304 m², and one square metre is about 10.764 ft². One square yard is 9 ft², or about 0.836 m².
Feet and inches
Tape measures in the US show feet and inches, often with fractions. The calculator turns 12’ 6” into 12.5 ft before multiplying. Doing this by hand is where many mistakes happen: 12 ft 6 in is 12.5 ft, not 12.6 ft.
Worked examples
Example 1: a simple bedroom (imperial)
A bedroom measures 12 ft by 15 ft.
- Area: 12 × 15 = 180 ft².
- In square metres: 180 × 0.09290304 = 16.72 m².
- In square yards: 180 ÷ 9 = 20 yd².
- With 10% flooring waste: 198 ft², so you would buy the number of packs that covers at least 198 ft².
Example 2: an L-shaped living room (subtract method)
The outer rectangle is 20 ft by 15 ft, with an 8 ft by 6 ft corner missing where the hallway cuts in.
- Outer rectangle: 20 × 15 = 300 ft².
- Missing corner: 8 × 6 = 48 ft².
- Total: 300 − 48 = 252 ft², or 23.41 m².
In the calculator, enter the 20 × 15 rectangle, then add a second rectangle of 8 × 6 with Mode set to Subtract.
Example 3: a room with a sloping wall (metric)
A kitchen is 4.2 m by 3.6 m, with an extra triangular area 2.4 m along the base and 1.2 m deep where one wall angles out.
- Rectangle: 4.2 × 3.6 = 15.12 m².
- Triangle: ½ × 2.4 × 1.2 = 1.44 m².
- Total: 16.56 m², or about 178.25 ft².
Regional notes
US floor area is quoted in square feet, with ANSI Z765 used to measure finished homes. UK listings quote both ft² and m², and Energy Performance Certificates use m². In Australia a traditional “square” is 100 ft² (about 9.29 m²), and Canadian listings and flooring retailers commonly use square feet despite metric standards.
Tips and common mistakes
- Measure at more than one point; walls are rarely parallel. Use the larger figure when buying.
- Include closets and alcoves if they get the same flooring.
- Round up packs, not area: add waste, divide by pack coverage, then round up.
- Walls? Use the paint calculator. Volume? Use the cubic yard calculator.
Plan the rest of the project
Once you have the area, price flooring with the flooring calculator, tile with the tile calculator, turf with the sod calculator, or total several boards and runs with the linear feet calculator.
Frequently asked questions
How do I calculate square footage?
For a rectangle, multiply the length in feet by the width in feet. A room 12 ft by 15 ft is 180 square feet. For other shapes, split the space into rectangles and triangles, work out each area and add them together.
How do I convert square feet to square metres?
Multiply square feet by 0.09290304, which is exact because a foot is defined as 0.3048 m. To go the other way, divide square metres by 0.09290304, or multiply by about 10.764.
How do I measure an L-shaped room?
Either split it into two rectangles and add them, or measure the full outer rectangle and subtract the missing corner. Both give the same answer; the calculator's Subtract mode handles the second approach.
How do I enter feet and inches?
Type them as 12' 6", 12ft 6in, or just 12 6 with a space. You can also use decimal feet such as 12.5. Fractions like 4 1/2 inches work too.
Should I measure wall to wall or include skirting boards?
For flooring, measure the floor wall to wall at floor level. Skirting boards (baseboards) sit on top of the flooring edge, so their thickness does not need to be subtracted.
How much extra flooring should I buy?
Many manufacturers and fitters suggest 5 to 10% extra for straight-laid flooring and more for diagonal or herringbone patterns, to allow for cuts and future repairs. Check the installation guide for your product.
What is a square yard and when is it used?
A square yard is 3 ft by 3 ft, or 9 square feet. In the US, carpet has traditionally been priced per square yard, so divide square feet by 9 to compare prices.
Why does my house's listed square footage differ from my measurements?
Different measuring standards include or exclude different areas, such as wall thickness, stairs, garages and spaces with low ceilings. In the US, ANSI Z765 is a common standard for single-family homes; in the UK, RICS publishes measuring practice for surveyors. Your room-by-room total will usually be smaller than a gross figure measured to the outside of walls.
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Sources and references
About this calculator
Written and maintained by Rashid Mehmood, founder of CalcTen. The formulas are unit-tested against hand-worked examples, and the content is reviewed whenever product sizes or guidance change. Last updated 1 November 2026. See our editorial policy.
Results are estimates for planning and ordering. Always check product labels, supplier advice and local building codes, and consult a qualified professional for structural work. Read the disclaimer.