How to Calculate Square Metres (m²)

The basic rule: length × width

Measure the length and width of the space in metres and multiply them. The answer is in square metres, written m². A patio that is 5 m long and 3.5 m wide is 5 × 3.5 = 17.5 m².

Measure along the floor or ground from wall to wall at the widest points, and measure each side twice. Walls and fences are rarely perfectly square, so take the longest measurement if the two ends differ.

If you measured in centimetres, feet or inches

Convert to metres before you multiply. To change centimetres to metres, divide by 100, so 350 cm is 3.5 m. One foot is 0.3048 m and one inch is 0.0254 m.

Alternatively, multiply in your own units and convert the answer. Square units do not convert like lengths, because the conversion applies to both sides. One square metre is about 10.764 square feet, so divide square feet by 10.764 to get square metres: 150 sq ft is about 13.9 m².

• 400 cm × 300 cm: 4 m × 3 m = 12 m²
• 13 ft × 10 ft = 130 sq ft ÷ 10.764 = about 12.1 m²
• 1 m² = 10.764 sq ft = 1.196 sq yd

L-shapes, alcoves and awkward rooms

Sketch the room and divide it into rectangles. Measure each one, work out its area and add them together. A 5 m by 4 m room with a 2 m by 1.5 m corner missing can be worked out in one go as 5 × 4 − 2 × 1.5 = 17 m².

Include alcoves, bays and doorway thresholds if they will be covered. Leave out areas that will not be, such as fitted kitchen units, following the instructions for the material you are buying.

Triangles and circles

For a triangle, multiply the base by the straight-line height and halve it. A triangle with a 6 m base and a 4 m height is half of 24, so 12 m². Use the straight-line height, not the length of a sloping side.

For a circle, use about 3.14 times the radius times the radius, where the radius is half the distance across. A circular bed 3 m across has a 1.5 m radius, so its area is 3.14 × 1.5 × 1.5 = about 7.07 m².

Turning area into something to buy

The area is the exact size of the space. Most materials also need an allowance for cuts, breakages and uneven ground, commonly around 10%. A 12 m² room therefore needs enough flooring to cover about 13.2 m².

The flooring, tile, paint and gravel calculators add that allowance and round up to whole packs, boxes, litres or bags, so use them once you know the area.