Key numbers
- Formula: length (m) × width (m) × thickness (cm) ÷ 100 = m³
- 1 m³ covers 10 m² at 10 cm, 6.67 m² at 15 cm
- 1 m³ ≈ 2,400 kg wet; 1 m³ = 1.308 yd³
- Bags: 1,000 ÷ bag yield in litres (17 L per 80 lb bag = 59 per m³)
On this page
- How to use the Concrete Calculator (Metric, m³)
- How to calculate cubic metres of concrete
- Cubic metres for common slab sizes
- Footings, columns and other shapes in m³
- How many bags make a cubic metre?
- Converting between m³ and cubic yards
- How much does a cubic metre of concrete weigh?
- Common metric estimating mistakes
- Frequently asked questions
How to use the Concrete Calculator (Metric, m³)
- 1Choose the shapePick slab / pad, monolithic slab, round slab, footing, column / sonotube, post holes, steps, wall, curb & gutter, square / rect. column, beam or hollow cylinder. Each shape uses its own volume formula.
- 2Pick your unitsEvery dimension has its own unit menu (in, ft, yd, cm or m); changing one converts that number so the size stays the same. The US / Metric switch sets all fields to feet and inches or meters and centimeters and resets them to typical values.
- 3Enter the dimensionsType the length (default feet), width (default feet) or thickness (default inches). Measure the inside of the forms and the depth in several places.
- 4Set waste and quantityUse the waste slider (0 to 20%, default 10%) and allow more on uneven ground. If you have several identical pours, enter how many.
- 5Read the resultsSee the volume in cubic yards, cubic feet and cubic meters, the ready-mix order rounded up to ¼ yard, the number of 90, 80, 60, 50 and 40 lb bags rounded up, and the weight at the density you choose (150, 145 or 140 lb/ft³).
- 6Price it and save itPick a pricing basis (per cubic yard, per cubic meter or per bag of the highlighted size) and enter your local price for a material cost. Use Add to project to total several pours, and Copy link to share the exact result.
Results update as you type. Back to the calculator ↑
How to calculate cubic metres of concrete
Concrete volume in metric is length × width × depth, all in metres. Thickness is usually given in centimetres, so divide it by 100 first, or use this version:
Cubic metres = length (m) × width (m) × thickness (cm) ÷ 100
The calculator above opens in metric (metres and centimetres) and covers slabs, footings, columns, post holes, steps, walls and curbs. Each field has its own unit menu if one measurement is in millimetres or feet.
- Measure inside the formwork in metres.
- Measure the depth in several places and use the average.
- Multiply or enter the numbers above.
- Add 10% for spillage and an uneven sub-base, then round up to what your supplier sells (often 0.1, 0.2 or 0.5 m³ steps; ask).
Worked example: 4 × 4 m slab, 10 cm thick
- 4 × 4 × 0.10 = 1.6 m³
- Add 10%: 1.76 m³ to order
- Wet weight at about 2,400 kg/m³: 3,844 kg
- In US units: 1.6 m³ = 2.09 yd³
Cubic metres for common slab sizes
Volumes for slab sizes people search for, with 10% extra and the in-place weight at 150 lb/ft³ (about 2,403 kg/m³).
| Slab | Thickness | m³ | m³ with 10% extra | Wet weight (kg) |
|---|---|---|---|---|
| 2 × 2 m | 10 cm | 0.40 | 0.44 | 961 |
| 3 × 3 m | 10 cm | 0.90 | 0.99 | 2,162 |
| 3 × 4 m | 10 cm | 1.20 | 1.32 | 2,883 |
| 4 × 4 m | 10 cm | 1.60 | 1.76 | 3,844 |
| 5 × 4 m | 10 cm | 2.00 | 2.20 | 4,806 |
| 5 × 5 m | 10 cm | 2.50 | 2.75 | 6,007 |
| 6 × 3 m | 15 cm | 2.70 | 2.97 | 6,487 |
| 6 × 6 m | 10 cm | 3.60 | 3.96 | 8,650 |
| 6 × 6 m | 15 cm | 5.40 | 5.94 | 12,975 |
| 10 × 5 m | 15 cm | 7.50 | 8.25 | 18,021 |
| 10 × 10 m | 15 cm | 15.00 | 16.50 | 36,042 |
Coverage per cubic metre is 100 ÷ thickness in cm: 10 m² at 10 cm, 8 m² at 12.5 cm, 6.67 m² at 15 cm and 5 m² at 20 cm. Thickness itself comes from your drawings and local building regulations, not from this table.
Footings, columns and other shapes in m³
The same rule works for every shape: area of the cross-section × length, in metres.
| Element | Size | m³ | m³ with 10% extra |
|---|---|---|---|
| Strip footing | 10 m × 45 cm × 20 cm | 0.90 | 0.99 |
| Strip footing | 20 m × 60 cm × 25 cm | 3.00 | 3.30 |
| Strip footing | 30 m × 60 cm × 30 cm | 5.40 | 5.94 |
| Round columns (4) | 30 cm Ø × 1.2 m | 0.339 | 0.37 |
| Round columns (6) | 25 cm Ø × 1.0 m | 0.295 | 0.32 |
| Post holes (10) | 20 cm Ø × 0.9 m | 0.283 | 0.31 |
| Curb + gutter | 15 × 45 cm + 60 × 15 cm, 100 m | 15.75 | 17.33 |
For a round column or hole, the cross-section is π × radius². A 30 cm diameter tube has a radius of 0.15 m, so π × 0.15² × 1.2 m = 0.085 m³ each. Select Column / Sonotube or Post holes in the calculator to do this automatically. For post holes it also subtracts the post.
How many bags make a cubic metre?
Divide 1,000 by the bag’s yield in litres. Bag yields are printed on the bag and data sheet and vary by product and country, so use the figure on yours.
Bags per m³ = 1,000 ÷ yield per bag (L)
- 80 lb (36.3 kg) QUIKRETE Concrete Mix: 17 L per bag → about 59 bags per m³.
- 60 lb (27.2 kg): 12.7 L → about 79 bags per m³.
- 40 lb (18.1 kg): 8.5 L → about 118 bags per m³.
So a 1.76 m³ order for the 4 × 4 m slab would be about 104 of the 80 lb bags. Above roughly 0.5 m³, a ready-mix delivery is usually far less work than hand mixing.
Converting between m³ and cubic yards
Ready-mix in the US is sold by the cubic yard; most of the world uses cubic metres. NIST gives the exact factor:
| From | To | Multiply by | Example |
|---|---|---|---|
| m³ | yd³ | 1.308 | 2 m³ = 2.62 yd³ |
| yd³ | m³ | 0.7646 | 5 yd³ = 3.82 m³ |
| m³ | ft³ | 35.31 | 1.6 m³ = 56.5 ft³ |
| m³ | litres | 1,000 | 0.3 m³ = 300 L |
For bigger conversion jobs, use the cubic yard calculator.
How much does a cubic metre of concrete weigh?
About 2,400 kg for normal-weight concrete. US highway and bridge references put normal concrete at roughly 140–155 lb/ft³, which is about 2,240–2,480 kg/m³; the calculator lets you pick 150, 145 or 140 lb/ft³. Lightweight mixes weigh less. Your supplier can give the density of the mix it delivers. For full tonnage tables use the concrete weight calculator.
Common metric estimating mistakes
- Multiplying centimetres as metres. 4 × 4 × 10 = 160 is not cubic metres. Divide the 10 cm by 100: 1.6 m³.
- Mixing millimetres and centimetres. 100 mm = 10 cm = 0.10 m.
- No allowance. Add about 10% for spillage and an uneven sub-base.
- Using a US bag yield abroad. Bag sizes and yields differ by country; read the bag.
For US units (feet, inches and cubic yards), use the concrete slab calculator or the homepage concrete calculator.
FAQ
Frequently asked questions
How many m3 of concrete do I need for a 4x4 slab?
1.6 m³ for a 4 × 4 m slab 10 cm thick, or 1.76 m³ with 10% extra. At 15 cm it needs 2.4 m³ (2.64 m³ with extra). The wet concrete weighs about 3,850 kg at 10 cm.
How many m3 of concrete for a 3x3 slab?
0.9 m³ at 10 cm thick, 0.99 m³ with 10% extra. A 3 × 4 m slab at 10 cm needs 1.2 m³ (1.32 m³ with extra) and a 5 × 5 m slab 2.5 m³ (2.75 m³).
How many square metres does 1 m3 of concrete cover?
10 m² at 10 cm thick. Divide 100 by the thickness in centimetres: 1 m³ covers 8 m² at 12.5 cm, 6.67 m² at 15 cm and 5 m² at 20 cm.
How do you calculate cubic metres of concrete?
Convert every dimension to metres and multiply: length × width × depth. Centimetres divide by 100, so 15 cm is 0.15 m. A 6 × 6 m slab 15 cm thick is 6 × 6 × 0.15 = 5.4 m³.
How many bags of concrete make 1 cubic metre?
Divide 1,000 by the bag's yield in litres. An 80 lb QUIKRETE bag yields 17 L, so about 59 bags make 1 m³; a 60 lb bag (12.7 L) needs about 79. Use the yield printed on your bag.
How much does 1 m3 of concrete weigh?
About 2,400 kg for normal-weight concrete (150 lb/ft³). Published unit weights run from roughly 2,240 to 2,480 kg/m³ (140–155 lb/ft³), so ask your supplier for its mix.
How many cubic yards is 1 cubic metre?
1 m³ = 1.308 yd³, and 1 yd³ = 0.7646 m³ (NIST). A 2 m³ order is 2.62 yd³; a 5 yd³ US order is 3.82 m³.
How much concrete for a strip footing in m3?
Length × width × depth. A 10 m footing 45 cm wide and 20 cm deep needs 0.9 m³ (0.99 m³ with 10% extra). A 20 m run at 60 × 25 cm needs 3 m³.
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Last reviewed October 12, 2026 by M Bilal. Found an error? Tell us.