How to calculate square footage
Square footage is simply area — the amount of surface a space covers, measured in square feet (ft²) or square metres (m²). To calculate the square footage of a room you multiply its width by its length; a 12 ft by 15 ft room is 12 × 15 = 180 square feet. The calculator above does this for you and handles the shapes a tape measure alone can't: L-shaped rooms, circles, triangles, and areas you already know.
Add a region for each part of the job, choose its shape, and type the measurements. Each region shows its own area and a live scaled diagram, and the total updates as you go. Because the tool stores one canonical measurement internally, you can switch between imperial and metric at any time and read the same area converted across square feet, square metres, square yards, acres and hectares.
Area formulas by shape
Every region is just one of a handful of area formulas. Pick the shape that matches what you are measuring and the calculator applies the right one:
Rectangle: area = width × length. L-shape: take the full outer rectangle and subtract the missing corner — area = full width × full length − notch width × notch length. Circle: area = π × (diameter ÷ 2)². Triangle: area = base × height ÷ 2. Already know the number? Choose “Known area” and type the square footage straight in — handy when a floor plan or listing already quotes it and you only need the conversions, waste and cost.
Each region uses the formula for its shape. The width, length and other dimensions you enter feed straight into it.
Rectangle
Area = width × lengthL-shape
Area = full width × full length − notch width × notch lengthCircle
Area = π × (diameter ÷ 2)²Triangle
Area = base × height ÷ 2Worked examples
Three common jobs, worked end to end. The same live diagram that draws them in the calculator renders them here.
Three worked jobs, each drawn to scale with its calculation.
L-shaped living room
- Given
- Full room 5 m × 4 m
- Kitchen bay notched out 2 m × 1.5 m
- Working
5 × 4 − 2 × 1.5 = 20 − 3- Result
- 17 m² (≈ 183 ft²)
Circular patio
- Given
- Diameter 4 m
- Working
π × (4 ÷ 2)² = π × 2²- Result
- 12.57 m² (≈ 135 ft²)
Triangular gable end
- Given
- Base 6 m
- Height 2.5 m
- Working
6 × 2.5 ÷ 2- Result
- 7.5 m² (≈ 81 ft²)
Waste and cost
The net area is what your space actually measures, but it is rarely what you buy. Cuts, offcuts, breakage and pattern matching all mean you order more than the bare area. Add a waste percentage — commonly 5–10% for simple layouts and 10–15% for diagonal or patterned work — and the calculator shows the “area to order” including that allowance.
Enter a price per square foot or per square metre and it multiplies the area-with-waste by that rate to estimate a material cost. Both the waste and the price are optional: leave them blank and the tool just reports the net area and its conversions. The cost is always based on the area you would order, not the bare area, so the estimate matches what you would spend at the counter.
Converting area units
Area units convert by the square of the length conversion. Because one foot is 0.3048 metres, one square foot is 0.3048² = 0.092903 square metres, and one square metre is 10.7639 square feet. The calculator converts the total for you, but the reference below is useful for sanity-checking a figure by hand.
Larger parcels are quoted in square yards, acres and hectares; roofers and siding crews often work in “squares” of 100 ft². The conversion readout in the results panel shows all of these at once.
| Unit | Equivalent |
|---|---|
| 1 square metre (m²) | 10.7639 ft² |
| 1 square foot (ft²) | 0.092903 m² |
| 1 square yard (yd²) | 9 ft² = 0.836127 m² |
| 1 acre | 43,560 ft² = 4,046.86 m² |
| 1 hectare | 10,000 m² = 2.4711 acres |
| 1 square (roofing / siding) | 100 ft² = 9.2903 m² |
How this calculator works
Describe each region by its shape and dimensions rather than a raw number, so a unit mix-up can't silently distort the result. The tool sums the valid regions into a net total, shows that total converted across the common area units, and — optionally — applies a waste percentage and a price per unit to estimate what you would actually buy.
Everything is calculated on your device: nothing you type is uploaded, and your project is saved only in your own browser. Export the breakdown to CSV or print a clean takeoff when you are done.
Using the square footage calculator
- Choose your unitsSwitch the units control to metric or imperial. You can change it at any time and every value converts.
- Add a region for each areaStart with the seeded region and use “Add region” for each separate space or part of the job.
- Pick each region's shapeChoose rectangle, L-shape, circle, triangle or known area. The input fields and diagram change to match.
- Enter the dimensionsType the measurements. Each region shows its own area and a scaled diagram, and the total updates live.
- Read the total and conversionsThe results panel shows the total area in your unit plus conversions to m², ft², yd², acres and hectares.
- Add waste and priceOptionally add a waste percentage and a price per unit to see the area to order and an estimated cost.
- Export or move onExport a CSV, print a takeoff, or follow a material link to turn the area into a bill of materials.
Frequently asked questions
Common questions about measuring area and square footage.
What is square footage?
Square footage is the area of a surface measured in square feet (ft²). A square foot is a square one foot on each side. Area equals length times width for a rectangle, so a room 10 ft by 12 ft is 120 square feet.
How do I calculate the square footage of a room?
Measure the width and the length in the same unit and multiply them. For a rectangular room that is width × length. For irregular rooms, split them into rectangles or use the L-shape, circle or triangle options and the calculator sums the parts for you.
How do I find the area of an L-shaped room?
Measure the full outer rectangle, then measure the missing corner (the notch). The area is full width × full length − notch width × notch length. Choose the L-shape option and enter both pairs; the diagram shows the notch removed from the top-right corner.
How do I calculate the area of a circle?
Measure the diameter across the widest point. The area is π × (diameter ÷ 2)², which is π times the radius squared. A 4 m circle is π × 2² ≈ 12.57 m².
How do I calculate the area of a triangle?
Measure the base and the perpendicular height (straight up from the base to the opposite point). The area is base × height ÷ 2. A 6 m base with a 2.5 m height is 6 × 2.5 ÷ 2 = 7.5 m².
How do I convert square feet to square metres?
Multiply square feet by 0.092903 to get square metres, or multiply square metres by 10.7639 to get square feet. The calculator shows both at once, so you rarely need to do it by hand.
How many square feet are in an acre?
An acre is 43,560 square feet, which is about 4,046.86 square metres. A hectare is 10,000 square metres, or about 2.47 acres. The conversion readout shows acres and hectares for larger parcels.
Should I add a waste allowance?
Usually yes. Cuts, offcuts and breakage mean you buy more than the bare area — commonly 5–10% for simple layouts and 10–15% for diagonal or patterned work. Enter a waste percentage and the tool shows the area to order including it.
Is the calculator free and private?
Yes. It is completely free and runs entirely in your browser — nothing you type is uploaded. Your project is saved only on your own device, and you can export it to CSV or print it at any time.