Cubic metre calculator for skips and deliveries

How to work out cubic metres: the sum

Multiply length by width by height, all in metres, and the answer is in cubic metres (m³). For a slab or a dig, the height is the depth, so 150mm goes in as 0.15m. Times the m³ by 1,000 for litres. Times it by the material's density in tonnes per m³ for the weight you will be ordering or carting away.

The calculator opens on a driveway sub-base: 6m long, 3m wide and 150mm deep, in MOT Type 1.

• Volume: 6 × 3 × 0.15 = 2.7m³.
• In litres: 2.7 × 1,000 = 2,700 litres.
• In cubic feet: 2.7 ÷ 0.0283168 = 95.35ft³.
• In cubic yards: 2.7 ÷ 0.7645549 = 3.53yd³.
• Weight: 2.7 × 2.2 tonnes per m³ = 5.94 tonnes of Type 1.

Boxes, cylinders and slabs

Three shapes cover most of what gets dug, poured or filled on a job. The How many box multiplies the answer, so six identical post holes are one entry, not six.

Cubic metres to tonnes: it depends what's in it

A cubic metre of water weighs a tonne. Almost nothing on a building site does. Multiply the m³ by the material's density to get tonnes, and the density changes a lot from one material to the next. These are the figures the calculator uses. Each comes from a UK supplier. The tool does not let you change them, so if your own supplier quotes a different density, multiply the m³ by theirs.

• Concrete: 2.4t per m³. Tarmac gives 2.3 to 2.4t for a cubic metre of standard concrete, and 2.4 is used here.
• MOT Type 1: 2.2t per m³. The factor in Breedon's aggregates calculator, applied to the depth you measure once it is laid. Loose in a bag it is lighter.
• Sand and cement screed: 2.0t per m³. Flowcrete's K-Screed data sheet gives its K-Screed, a semi-dry screed laid with sand, a density of about 1.8 to 2.0t per m³, and the higher one is used here.
• Sharp sand: 1.7t per m³. M&P Moran describes its sharp sand bulk bag as about 0.5m³ and 800 to 850kg. Divide one by the other and you get 1.6 to 1.7t per m³.
• Gravel: 1.6t per m³. Carvers uses 1.6 for standard gravel, 1.75 for crushed and 1.5 for decorative.
• Topsoil: 1.5t per m³. Rolawn says a tonne of standard topsoil is about 0.67m³, and 1 ÷ 0.67 is 1.49.

Skips and muck-away: allow for bulking

Ground swells when you dig it. A hole that measures 4.5m³ does not fit in a skip that holds 4.5m³, because broken-up soil takes more room than it did packed in the ground. Work out the dig in m³, add the bulking, then turn it into cubic yards, which is how UK skips are named.

The British Geological Survey groups bulking by material: sand, gravel and soft clay or silt swell by 5 to 20%; firm clay and silt by 20 to 40%; weak rock by 40 to 55%. Put your figure in the Bulking once dug box and the calculator adds a loose volume, in m³, beside the dug volume. The weight does not change when soil bulks, so the tonnes stay the same.

Take a dig for a driveway 6m by 3m, down 250mm into firm clay. That is 4.5m³ in the ground. At 30% bulking it becomes 5.85m³ loose. The tool gives the loose figure in m³ only; divided by 0.7646, it is 7.65 cubic yards.

• Skip sizes in m³: a cubic yard is 0.9144 × 0.9144 × 0.9144 = 0.7646m³, so a 2-yard skip holds 1.53m³, a 4-yard 3.06m³, a 6-yard 4.59m³ and an 8-yard 6.12m³.
• Heavy waste: ISM Waste says a 6-yard skip is the largest that can be filled entirely with heavy waste such as soil, rubble and bricks. On that firm's rule, the 7.65 yards of clay above needs two 6-yard skips, not one 8-yard.
• Weight on the lorry: soil dug from the ground is denser than the screened topsoil a supplier delivers, so the topsoil figure will understate it. Ask the muck-away firm what weight per load they work to, and use their figure rather than the tool's tonnes.

Ordering a delivery by the cubic metre

Merchants sell aggregates by the tonne, by the bulk bag or by the loose load, and ready-mix concrete by the m³. Work out the m³ here, then check how your supplier sells it. A bulk bag sold as a tonne bag usually holds nearer half a cubic metre, like the sand bag above.

The Add for waste box adds a percentage to the volume and the tonnes, for spillage, uneven ground and compaction. It starts at 0%, so you see the bare volume first. Each material calculator applies its own allowance and rounds up to whole bags and loads:

Where the numbers can be off

It measures regular shapes from the sizes you give it. Real digs and bases are rarely perfectly level, and a slab that is 10mm deeper than planned over a large area adds up fast. Take several depth readings and use the average, or the deepest if you would rather not run short.

• Densities are typical, not certified. Moisture, grading and the quarry all change them. The supplier's weighbridge ticket is the real figure.
• No compaction maths. Type 1 is ordered by the compacted depth here. The Type 1 calculator handles the extra for compaction.
• Skip rules vary. Weight limits, what counts as heavy waste and how full you may load a skip are set by each hire firm. Check before you book.
• Freight is different. Couriers and shippers work in cubic metres too, but they also charge by volumetric weight, which this does not calculate.

Common questions