Area formulas
All measurements are converted to metres before calculating, so you can measure in cm, mm, feet or inches. For irregular rooms, split the space into simple shapes, work out each one and add them up using the "Number of identical areas" box or a running total.
Common conversions
| Square metres | Square feet | Square yards |
|---|---|---|
| 1 m² | 10.76 ft² | 1.20 yd² |
| 10 m² | 107.6 ft² | 11.96 yd² |
| 25 m² | 269.1 ft² | 29.90 yd² |
| 100 m² | 1,076 ft² | 119.6 yd² |
Measuring tips
- Measure each wall at floor level, in two places if the room may not be square, and use the larger figure.
- For flooring and tiles, include areas under fitted units only if the floor will go underneath.
- Always add 5–10% when ordering materials to allow for cuts and waste.
Worked examples
A rectangular room: 4.2m × 3.5m = 14.7m², or 158.2ft². With 10% extra for flooring cuts, order 16.2m².
An L-shaped kitchen: measure the full outer length and width, 4.2m × 3.5m, then the missing corner, 1.5m × 1m. The area is 14.7 − 1.5 = 13.2m². Choose L-shape above and enter the cut-out to get the same answer.
A room measured in feet: 12ft × 10ft = 120ft². Each side converted to metres is 3.658m × 3.048m = 11.15m². Choose "Feet" as the unit and the calculator converts for you. Don't divide 120 by 10 as a shortcut: that would give 12m², almost 8% too much.
Floors, walls and ceilings need different areas
- Floors and ceilings: length × width, as above. Ceiling area is the same as floor area unless the ceiling slopes.
- Walls: add the wall lengths to get the perimeter, multiply by the height, then take off doors (about 1.6–1.9m² each) and windows. The paint calculator and wallpaper calculator do this from the room size.
- Edges: skirting, edging and fencing are bought by length, not area. The perimeter shown in the result is the starting point for the skirting board calculator.
- Slopes: a sloping garden or roof has more surface than its plan size suggests. For roofs, the roof tile calculator adds the pitch for you.
Common measuring mistakes
- Mixing units. A width of 350cm entered as metres becomes 350m. Pick the unit you measured in and keep both sides in it.
- Converting area like length. 1m = 100cm, but 1m² = 10,000cm². Converting each side first, as the calculator does, avoids the trap.
- Trusting floor plans. Estate agent plans are often rounded and may include wall thickness or exclude bay windows. Measure the actual room before ordering.
- Forgetting alcoves and bays. Measure them as separate rectangles and add them. Use "Number of identical areas" when you have several the same size.
Once you have the area, use it in the flooring, tile or turf calculators. For other conversions such as cubic metres, gallons or slopes, see the construction unit converter.