How to calculate square metres – an easy guide with examples

Whether you are laying paving, sowing a new lawn or ordering gravel for the driveway, it all starts with the same question: how many square metres is the area? A square metre (m²) is a measure of area – in other words, how large a surface is.

In this guide we show how to easily calculate square metres for all kinds of shapes, and how to then convert to m³ and litres so you can order the right quantity of materials.

How to calculate square metres - maxibag.dk

How to calculate square metres for a rectangle

A rectangular or square area is the easiest to calculate:

Length (m) × width (m) = square metres (m²)

Example: A patio is 6 metres long and 4 metres wide: 6 × 4 = 24 m².

Remember to measure in metres. If you have measured in centimetres, divide by 100 first: 350 cm = 3.5 m.

Triangles and circles

Triangle: Multiply the base by the height and divide by 2.

Base (m) × height (m) ÷ 2 = m²

Example: A triangular bed with a base of 4 metres and a height of 3 metres: 4 × 3 ÷ 2 = 6 m².

Circle: Multiply the radius (half the diameter) by itself, and multiply by 3.14.

3.14 × radius × radius = m²

Example: A round bed with a diameter of 3 metres has a radius of 1.5 metres: 3.14 × 1.5 × 1.5 = approx. 7.1 m².

How to calculate irregular areas

Most gardens and driveways are not perfectly rectangular. In that case, divide the area into smaller, simple shapes:

Draw the area on a piece of paper and divide it into rectangles and triangles.
Measure each shape separately.
Calculate the area of each shape.
Add the figures together.

Example: An L-shaped driveway can be divided into two rectangles: 8 × 3 m = 24 m² and 4 × 3 m = 12 m². Together 36 m².

If you need to subtract something – e.g. a bed in the middle of a lawn – calculate it separately and subtract it from the total area.

From square metres to m³ and litres

Square metres tell you how large the area is. When ordering soil, gravel, sand or mulch, you also need to know the layer depth – that gives you the volume in cubic metres (m³):

Square metres (m²) × layer depth (m) = cubic metres (m³)

1 m³ equals 1,000 litres.

Example: A new lawn of 50 m² with 10 cm of topsoil needs 50 × 0.10 = 5 m³ = 5,000 litres.

See the recommended layer depths for the most common projects in our guide How much gravel, sand and soil do I need?.

Examples from the garden

Gravel driveway: 6 × 5 m = 30 m². With 18 cm of road base as a sub-base: 30 × 0.18 = 5.4 m³. Read more in our guide Gravel for driveways.
Paved patio: 5 × 4 m = 20 m². See how to build the base in How to Prepare the Base for Paving.
Bed with granite chippings: A round bed with a diameter of 2 m: 3.14 × 1 × 1 = 3.14 m². With 5 cm of granite chippings: 3.14 × 0.05 = approx. 0.16 m³ = 160 litres.
Sandpit: 2 × 2 m = 4 m². With 30 cm of sand: 4 × 0.3 = 1.2 m³. See more in our guide to sandpit sand.

Tips when measuring

Use a long tape measure or a laser measure – and measure twice.
Measure in metres to one decimal place, e.g. 4.3 m. That is precise enough for garden projects.
Round up, not down. It is better to have a little material left over than to run short.
Add 10-20 % for materials that need compacting, e.g. road base.

If you would rather skip the maths, use our quantity calculator, where you simply enter the dimensions and layer depth.