Concrete quantity calculator
Estimate concrete for a slab, pad, wall or column and whole bags from your bag yield; a 4 × 3 m slab, 0.15 m thick, with 10 % waste needs 1.98 m³.
- Runs in your browser
- No upload
- Instant result
Quantity estimate only. This does not approve structural safety, load capacity, drainage, fire resistance or building-code compliance. Verify the design and local requirements with a qualified professional. Purchase quantities round up to whole packs.
Assumptions & formula
Formula and assumptions
w = Waste allowance/100; V=ΣLWH; V=π(d/2)²h×n; N=ceil(V(1+w)/Y)
The prefilled values are editable examples, not product specifications. Enter your supplier’s yield, density, coverage and packaging values, and add an allowance for overlaps, compaction and cuts where needed.
Purchase counts use the exact entered decimals and unit factors, without a rounding tolerance that could discard a real remainder. π and irrational square roots use enclosing bounds; ambiguous counts produce an error. Counts must be safe integers.
Results
Enter values and press Calculate to see the result here.
How to use this calculator
- Set inputs and units
Choose slab, pad, wall or cylindrical column. Enter the geometry, the allowance and the supplier’s bag yield in m³.
- Calculate
Check this worked example: slab: areas=4×3+2×2 m², opening=1×1 m², depth=0.2 m, waste=0%, bagYield=0.02 m³ → 3 m³,150 bags
- Results
Compare the net volume, the allowance volume and the whole bags. Bag counts are rounded up after the yield is applied.
Questions and limits
Is bag mass the same as bag yield?
No. Supply the volume of mixed concrete per bag, not kilograms, and get the product’s actual yield from its supplier.
Which input errors should I correct?
Use positive depth and yield and consistent geometry units. Openings can't be larger than the gross slab area.
What does this calculation leave out?
A quantity estimate only. It includes no mix design, reinforcement, strength, curing plan or foundation approval.