How to calculate square metres
Square metres measure area — how much floor, wall or ground a space covers. You need the figure to buy flooring, tiles, paint, turf or insulation, and to compare room sizes. This square meter calculator works it out for rectangles, triangles and circles, converts between metres, centimetres, feet and inches, and adds several areas together.
Rectangles and squares
Area = length × width. A room 4m long and 3.5m wide is 4 × 3.5 = 14 m². Measure wall to wall at floor level, and take the longest and widest points if the walls are not quite straight.
Triangles
Area = ½ × base × height, where the height is measured at right angles to the base. A triangle with a 3m base and 2m height covers 3 m². Gable walls and angled corners often include one.
Circles
Area = π × radius². Measure across the middle for the diameter and halve it. A circular patio 3m across covers about 7.07 m².
Measuring an L-shaped or awkward room
Split it into rectangles
Divide the room into simple shapes that do not overlap, work out each one and add them. An L-shaped room made of a 4m × 3.5m section and a 2m × 1.5m alcove is 14 + 3 = 17 m². Add each part as its own area above and the calculator totals them.
Bay windows and chimney breasts
Treat a bay as a rectangle plus two triangles, or a rectangle if it is shallow. Subtract a chimney breast or built-in cupboard only if the flooring will not go under it. For ordering materials, a slightly generous figure is safer than a tight one.
Converting between metres and feet
Useful when a floor plan, estate agent listing or product is in a different unit.
| You have | Calculation | Result |
|---|---|---|
| 14 m² | 14 × 10.764 | 150.69 sq ft |
| 150 sq ft | 150 ÷ 10.764 | 13.94 m² |
| A 13ft × 11ft room | 143 sq ft ÷ 10.764 | 13.29 m² |
| 350cm × 280cm | 3.5m × 2.8m | 9.80 m² |
| 14 m² | 14 × 1.196 | 16.74 sq yd |
1 m² is 10,000 cm². Multiplying centimetres and forgetting to divide by 10,000 is the most common measuring mistake.
From square metres to materials
Flooring and tiles
Add wastage for cuts: 10% for most rooms, 15% for diagonal or herringbone layouts. The 14 m² room needs 15.4 m² ordered; the 17 m² L-shaped room needs 18.7 m². Price it with the flooring calculator or the tile calculator.
Walls and paint
Wall area is the room’s perimeter × ceiling height. The 4m × 3.5m room has a 15m perimeter, so 2.4m walls cover 36 m². Turn that into litres and tins with the paint calculator.
Gardens and bases
Turf, gravel and slabs are all ordered by area too. For a concrete base, you also need the depth to get a volume — the concrete calculator takes it from there.
Measuring tips
- Use a tape or laser measure, and measure each wall twice
- Write measurements on a rough sketch as you go
- Stick to one unit for the whole room
- Round up to the nearest centimetre, not down
Square metre and square meter are the same thing — metre is the UK spelling. For what each square metre of floor actually costs, see UK flooring costs per m².