Show the math
- Convert to feet (inches ÷ 12, centimeters ÷ 30.48): Length 5 m = 16.4042 ft; Width 4 m = 13.1234 ft; Thickness 100 mm = 0.3281 ft
- Volume = 16.4042 × 13.1234 × 0.3281 × 1 = 70.6293 ft³
- Net volume = 70.6293 ft³ ÷ 27 = 2.6159 yd³ (× 0.0283168 = 2 m³)
- Order quantity = 2.6159 yd³ × (1 + 10%) = 2.8775 yd³ = 77.6923 ft³
- 80 lb bags = 77.6923 ft³ ÷ 0.6 ft³ per bag = 129.49 → 130 bags (always round up)
- Weight = 77.6923 ft³ × 150 lb/ft³ = 11,654 lb
How to measure
Measure the length and width of the formwork in meters, and the thickness in millimeters or centimeters. Thickness is the dimension most often confused: 100 mm is 0.1 m, not 1 m. The calculator converts each unit exactly, so you can leave dimensions in whichever unit you measured.
For slabs poured over a rough or sloping base, take several thickness readings and use their average.
The cubic meter formula
Work in meters and multiply: length × width × thickness. Convert thickness from millimeters by dividing by 1,000, so 100 mm is 0.1 m. The answer is cubic meters. Plants sell ready-mix by the cubic meter, often in steps of 0.5 m³ and with a minimum load size, so round your answer up and ask the plant for its minimum.
Add a waste allowance. In metric countries 5 to 10% is typical for a slab on a prepared base, and more for trench footings, where the excavation is rarely neat.
Formula: V (m³) = L (m) × W (m) × T (m) × quantity × (1 + waste%).
Worked example: 5 × 4 m slab, 100 mm thick
- Convert to feet (inches ÷ 12, centimeters ÷ 30.48): Length 5 m = 16.4042 ft; Width 4 m = 13.1234 ft; Thickness 100 mm = 0.3281 ft
- Volume = 16.4042 × 13.1234 × 0.3281 × 1 = 70.6293 ft³
- Net volume = 70.6293 ft³ ÷ 27 = 2.6159 yd³ (× 0.0283168 = 2 m³)
- Order quantity = 2.6159 yd³ × (1 + 10%) = 2.8775 yd³ = 77.6923 ft³
- 80 lb bags = 77.6923 ft³ ÷ 0.6 ft³ per bag = 129.49 → 130 bags (always round up)
- Weight = 77.6923 ft³ × 150 lb/ft³ = 11,654 lb
| Quantity | Result |
|---|---|
| Net volume | 2.616 yd³ (70.63 ft³, 2.000 m³) |
| Order with 10% waste | 2.88 yd³ (2.20 m³) |
| 80 lb bags | 130 |
| 60 lb bags | 173 |
| Weight at 150 lb/ft³ | 11,654 lb |
You would order about 2.20 m³. In US units that is 2.88 yd³ or 77.69 ft³. At 150 lb/ft³ (about 2,400 kg/m³) the order weighs 5,286 kg.
Concrete per square meter
| Thickness | m³ per m² | Area per m³ |
|---|---|---|
| 75 mm | 0.075 | 13.33 m² |
| 100 mm | 0.100 | 10.00 m² |
| 125 mm | 0.125 | 8.00 m² |
| 150 mm | 0.150 | 6.67 m² |
| 200 mm | 0.200 | 5.00 m² |
The table is useful for quoting a floor by area: a 100 mm slab uses 0.1 m³ for every square meter, so 1 m³ covers 10 m². At 150 mm it covers only 6.67 m².
Converting between metric and US volumes
| From | To | Multiply by |
|---|---|---|
| m³ | yd³ | 1.30795 |
| m³ | ft³ | 35.3147 |
| m³ | litres | 1,000 |
| yd³ | m³ | 0.764555 |
| ft³ | m³ | 0.0283168 |
| kg/m³ | lb/ft³ | 0.062428 |
The foot-to-meter factor is exact (0.3048 m), and the cubic factors follow from it. See the methodology page for the sources.
Cement, sand and gravel by volume
If you are mixing on site rather than ordering a truck, the mix ratio calculator turns a cubic meter of concrete into cement bags, sand and gravel. It uses the standard dry-volume factor of about 1.54, because the dry materials occupy more space than the wet concrete they make.
Mistakes with metric volumes
- Entering thickness in meters when you measured millimeters.
- Mixing meters and centimeters in one calculation.
- Forgetting that 1 m³ is not 1 yd³. A cubic meter is 1.31 cubic yards.
- Ordering exactly the net volume with no allowance for the base and the forms.
- Not accounting for the minimum load charged by the plant.
Ordering by the cubic meter
In most countries plants sell concrete in cubic meters, often in half-meter steps. State the quantity, the strength class (such as C25/30) and the maximum aggregate size when you order, and ask about the minimum load and the delivery charge.
Frequently asked questions
How do I calculate cubic meters of concrete?
Multiply length, width and thickness in meters. A 5 × 4 m slab, 100 mm thick: 5 × 4 × 0.1 = 2 m³.
How many cubic meters in a cubic yard?
One cubic yard is 0.764555 m³. One cubic meter is 1.30795 yd³.
How much does a cubic meter of concrete weigh?
About 2,400 kg for normal-weight concrete, which is 150 lb/ft³. Real mixes range from about 2,240 to 2,400 kg/m³.
How much area does 1 m³ of concrete cover?
At 100 mm thick, 10 m². At 150 mm, 6.67 m². At 200 mm, 5 m².
How much waste should I add in metric?
Five to ten percent for slabs on a prepared base, more for trenches and uneven ground.
Does the calculator show US bag counts?
Yes. The result card includes 40, 50, 60 and 80 lb bag counts alongside the metric volume, because the same pages are used for US and metric projects.
Sources
Estimate only. Results depend on the numbers you enter, ground conditions and your supplier. For structural work consult a licensed engineer and follow local codes. Brand names such as Quikrete and Sakrete are used only to cite published product data. This site is not affiliated with any brand.