How to use the square footage calculator
- Choose Imperial (feet) or Metric (metres).
- For each part of the space, choose the shape and enter its measurements. Rectangles need length and width; triangles need base and height; circles need the diameter; trapezoids need both parallel sides and the height.
- Use Add another for each extra section. Set the count to 2 or more for identical sections, or to −1 to subtract a section.
- Add an extra allowance for waste if you are buying material.
- Enter a price per unit area in the takeoff table to get a cost estimate.
How the area formulas work
- Rectangle: length × width.
- Triangle: ½ × base × height.
- Circle: π × (diameter ÷ 2)².
- Trapezoid: ½ × (side a + side c) × height.
Each row’s area is multiplied by its count, the rows are added, and the waste percentage is applied to the total. The result is shown in both square feet and square metres, using the exact conversion 1 ft = 0.3048 m.
Worked examples
Rectangular bedroom. 12 ft × 10 ft = 120 ft² (11.15 m²). With 10% waste for laminate, buy enough for 132 ft².
L-shaped living room. Split it into 16 × 12 ft (192 ft²) and 8 × 6 ft (48 ft²). Total 240 ft². If a 4 × 3 ft hearth won’t be covered, add a row of 12 ft² with count −1 for a net 228 ft².
Metric patio with a round planter. A 5 × 4 m patio is 20 m². A planter 1.2 m across covers π × 0.6² = 1.13 m². Subtracting it leaves 18.87 m².
How to interpret the results
Use the net area for things priced by coverage, such as paint for ceilings, flooring, turf or sealant. Use the total including waste when buying materials that come in fixed pack sizes, then round up to whole packs.
Tips and common mistakes
- Measure to the wall, not the skirting, for flooring; measure inside the edging for paving.
- Check units. Mixing inches and feet is the most common error. Convert inches to decimal feet (6 in = 0.5 ft) or switch to metric.
- Draw a sketch and label each rectangle before you start; it is easy to count a corner twice.
- Round up packs, not area: work out the total area first, then divide by the pack coverage.
Assumptions and limitations
All shapes are treated as flat and level. For sloped roofs, use the roof pitch calculator, which converts a footprint into the true sloped area.