Formula
Depth in metres = depth millimetres ÷ 1,000. Base volume = length × width × depth. Concrete with allowance = base volume × (1 + waste percent ÷ 100).
Trades
Concrete Volume Calculator
Estimate concrete volume for slabs, footings and rectangular pours from length, width, depth and waste allowance.
Calculator
Working calculator
Live result1.320 m³1.200 m³ base volume + 10.0% allowance
Formula used
Depth in metres = depth millimetres ÷ 1,000. Base volume = length × width × depth. Concrete with allowance = base volume × (1 + waste percent ÷ 100).
This is the method behind the answer, so the result can be checked rather than simply trusted.What-if check
Depth and allowance sensitivity
Small depth changes can move the order quantity. Keep the neat measured volume separate from the allowance you choose for site tolerance.
| Depth | Volume with allowance | Change |
|---|---|---|
| 75 mm | 0.990 m³ | -0.330 m³ |
| 100 mm | 1.320 m³ | Current depth |
| 125 mm | 1.650 m³ | +0.330 m³ |
| Allowance | Order estimate | Extra over base |
|---|---|---|
| 0% | 1.200 m³ | 0.000 m³ |
| 5% | 1.260 m³ | 0.060 m³ |
| 10% | 1.320 m³ | 0.120 m³ |
| 15% | 1.380 m³ | 0.180 m³ |
Visual proof
Slab prism
The prism shows why depth must be converted to metres before multiplying the three dimensions into cubic metres.
Printable calculation report
Result: 1.320 m³. Assumption: Length and width are entered in metres and depth is entered in millimetres.
- Length
- 4
- Width
- 3
- Depth
- 100
- Waste allowance
- 10
- Page/date context
- 2026-05-16 UTC page version
- Page URL
- https://calculationtime.com/calculators/concrete-volume-calculator
Worked example
For a 4 m by 3 m slab at 100 mm depth: depth = 100 ÷ 1,000 = 0.10 m. Base volume = 4 × 3 × 0.10 = 1.20 m³. With 10% allowance, 1.20 × 1.10 = 1.32 m³.
Professional note
Master’s Tip: measure the average finished depth separately from the excavation depth. For real orders, round up after checking site variation, formwork, sub-base level, pump/driver advice, minimum delivery quantities and whether part loads are practical.
Regional and unit assumptions
Standard or basis: this page uses transparent rectangular-volume arithmetic in SI metric units. One cubic metre is the volume of a cube one metre on each side; no concrete strength, mix design or compliance certification is claimed.
Assumptions and limitations
- Length and width are entered in metres and depth is entered in millimetres.
- The pour is treated as a rectangular prism with a consistent average depth.
- Waste allowance is a planning input only; it is not a building-code, engineering or supplier standard.
- The result does not check reinforcement, sub-base preparation, slump, strength grade, delivery minimums or structural design requirements.
Methodology & Accuracy
How this calculator is checked
CalculationTime pages are built around visible arithmetic: the formula, assumptions, worked example and practical limitations are shown so the result can be checked rather than simply trusted.
Formula used
Depth in metres = depth millimetres ÷ 1,000. Base volume = length × width × depth. Concrete with allowance = base volume × (1 + waste percent ÷ 100).
Standard or basis
Standard or basis: this page uses transparent rectangular-volume arithmetic in SI metric units. One cubic metre is the volume of a cube one metre on each side; no concrete strength, mix design or compliance certification is claimed.
Where a calculator follows a named legal, trade or industry standard, that standard is cited visibly. Otherwise the page uses transparent general arithmetic and states its limits.Master's Tip
Master’s Tip: measure the average finished depth separately from the excavation depth. For real orders, round up after checking site variation, formwork, sub-base level, pump/driver advice, minimum delivery quantities and whether part loads are practical.
Related calculators
Questions
How do I calculate concrete volume?
Convert the depth to metres, then multiply length × width × depth. Add any waste allowance after the base volume is visible.
How many cubic metres are needed for a 4 m by 3 m by 100 mm slab?
The base volume is 4 × 3 × 0.10 = 1.20 cubic metres. With a 10% allowance, the estimate becomes 1.32 cubic metres.
Should I add waste when ordering concrete?
Often yes for planning, but the right allowance depends on site level, excavation accuracy, spillage, delivery method and supplier advice. This page lets you test the percentage separately.
Does this choose the concrete mix strength?
No. It estimates volume only. Strength grade, reinforcement and structural requirements should be checked against the plans, engineer, builder or local code.
Can I use this for footings or trenches?
Yes for rectangular footings and trenches when length, width and average depth are known. Irregular shapes should be split into simpler sections and added together.
Calculation note
Concrete estimating is volume arithmetic before it is a material order. The calculator keeps the measured prism, depth conversion and allowance separate so a slab, footing or trench estimate can be checked line by line.
Concrete volume is a three-dimensional measurement
Area alone is not enough for a concrete pour. A slab needs length, width and depth, and the depth must be converted into the same unit as the other dimensions before volume is calculated.
Allowance belongs after the measured volume
Uneven ground, formwork variation, over-excavation, spillage and delivery handling can make the ordered quantity higher than the neat geometric volume. Keeping the allowance separate makes the assumption visible instead of hiding it in the measurement.
Volume is not structural approval
Knowing cubic metres does not decide concrete strength, reinforcement, curing, control joints or code compliance. Those choices depend on plans, engineering, site conditions and local building requirements.
Sources and further readingNIST: SI Units — LengthBIPM: SI BrochurePortland Cement Association: Concrete basics