Concrete calculator
Calculate concrete in cubic metres from metric dimensions and a visible allowance.
20 LAUNCH TOOLS
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When to use it
Use for a measured rectangular base after its purpose, finished dimensions and concrete specification have been established.
How it works
Net concrete = length × width × depth in metres; allowance is applied afterwards.
Worked example
Assume the checked inside formwork measures 4.0 m × 3.0 m, the selected project detail specifies 100 mm of concrete, and an illustrative 10% ordering allowance has been agreed. Convert 100 mm to 0.100 m: 4.0 × 3.0 × 0.100 = 1.20 m³ net; 1.20 × 1.10 = 1.32 m³. Confirm the supplier’s minimum load and sale increment before turning that estimate into an order.
Measurement guidance
Inside formwork length and width in metres, specified concrete depth in millimetres and a visible ordering allowance.
Buying and specification checks
The estimate assumes a rectangular, uniform concrete volume. It does not specify a suitable base, slab thickness, concrete, reinforcement, joints, sub-base, exposure class or curing period; obtain those project-specific inputs before ordering.
Measure the base and plan the pour
A correct volume is only one part of a workable concrete-base plan.
- Start with the structure or equipment that the base must support. Record the required footprint, finished level, clearances and the person or document that specifies the build-up; do not turn a convenient calculator depth into a structural decision.
- Measure the inside dimensions of the completed formwork, separate thickened edges or irregular shapes, and check diagonals, levels and any specified penetrations. Keep excavation, sub-base and concrete quantities distinct.
- Choose the supply route with the supplier or installer. Check minimum loads, ordering increments, vehicle size and reach, unloading point, pump or barrow route, placing time, washout arrangements, labour and what happens to unused concrete.
- Before delivery, confirm the prepared formation, compacted sub-base, membranes, formwork, reinforcement or joints where specified, safe access, tools, weather protection and curing materials. Wet concrete can cause serious cement burns and dermatitis: follow the product and HSE controls, avoid kneeling in it and provide suitable washing arrangements.
Common mistakes
- Ordering before checking levels
- Using excavation depth as slab thickness
- Treating volume as structural design
FREE TOOL AND PROJECT PACK
What the free calculator provides
The free calculator converts a measured rectangular footprint, specified concrete depth and visible allowance into an estimated cubic-metre quantity. It does not design the base, choose the concrete or plan delivery, placing or curing.
What the dedicated pack adds
The Concrete Base Project Pack helps plan and retain the wider ordinary small domestic base project.
- Purpose, site, size, level and full build-up decisions before buying.
- Concrete, excavation and material quantities, supply-route comparison, budget, access and a pour gate.
- Preparation, formwork, placing, curing, troubleshooting, handover and a retained base passport.
20-page printable digital workbook (PDF). Immediate digital delivery with 90-day access; no subscription.
Practical FAQs
Should I use excavation depth as concrete depth?
No. Enter the specified concrete thickness. Excavation can include sub-base, membranes, levelling and variable ground below the slab, so it needs a separate quantity and checked build-up.
Does 1.32 m³ mean I should order exactly 1.32 m³?
Not automatically. Confirm the allowance, minimum load, sale increment, access, placing method and handling of unused material with the supplier. Do not add the same allowance twice.
Does the calculator specify a suitable concrete base?
No. It estimates a rectangular volume from dimensions you enter. The supporting ground, sub-base, slab thickness, concrete specification, reinforcement, joints and loading need a suitable project-specific detail.
When can the concrete be loaded or the structure installed?
Use the concrete supplier’s and specification owner’s curing, protection and release advice for the actual mix, weather and load. Hard-looking concrete is not proof that it is ready, and there is no universal countdown for every base.
Planning guidance, not a quotation or a substitute for project-specific design and competent advice.