Concrete & Mortar Calculator
Estimate the concrete or mortar you need for a job. Enter the dimensions to get the volume, choose a mix, and the calculator estimates the cement, sand and aggregate, plus the number of cement bags. Every assumption is shown: the mix ratio, the dry-material bulking factor (dry ingredients occupy more loose volume than the finished mix), the cement bag size and the reference densities. Real quantities depend on your specific materials, compaction and wastage, so treat the figures as estimates and order a sensible margin over them.
How to use this tool
- Choose concrete or mortar, and your unit system.
- Enter the length, width and thickness (or depth) of what you are pouring.
- Pick the mix ratio appropriate to the job.
- Read the volume and the estimated cement, sand and aggregate, with the assumptions shown.
- Order a little extra — 5 to 10% — to cover wastage and uneven ground.
The formula
Concrete and mortar volume is simple geometry. Estimating the dry materials uses two labelled assumptions: a bulking factor (dry ingredients occupy more loose volume than the finished mix) and the mix ratio, which splits the dry volume into cement, sand and aggregate.
volume = length × width × thickness
dry_volume = volume × bulking_factor
part_volume = dry_volume × (part ÷ total_parts)- bulking factor
- ≈ 1.54 for concrete, 1.33 for mortar
- mix ratio
- Cement : sand : aggregate by volume
These are estimates from standard assumptions. Real quantities depend on the specific mix, aggregate grading, moisture and compaction, so order a margin over the estimate.
Worked examples
A small slab
- Given
- 5 × 4 × 0.1 m, M20
- Result
- 2 m³, ~16 bags cement
Volume is 2 m³; with the 1.54 bulking factor and 1:1.5:3 mix, that needs about 806 kg (16 bags) of cement, 0.84 m³ sand and 1.68 m³ aggregate.
Footing depth
- Given
- 10 × 0.3 × 0.6 m
- Result
- 1.8 m³
A strip footing 10 m long, 0.3 m wide and 0.6 m deep needs 1.8 m³ of concrete.
Brickwork mortar
- Given
- 0.5 m³, 1:4
- Result
- ~192 kg cement
Half a cubic metre of 1:4 mortar, with the 1.33 bulking factor, needs roughly 190 kg of cement and 0.53 m³ of sand.
Frequently asked questions
Because dry cement, sand and aggregate contain air and voids that disappear once mixed with water and compacted. The finished concrete is denser than the loose ingredients, so you need roughly 1.54 times the wet volume in dry materials. This bulking factor is a standard estimating assumption, shown in the results.
They are the ratio of cement to sand to aggregate by volume. A 1:2:4 mix (often called M15) is one part cement, two sand, four aggregate — a common general-purpose concrete. Lower sand and aggregate proportions (like 1:1.5:3) give stronger structural concrete; higher ones give weaker, cheaper fill.
They are good planning estimates from standard assumptions, but real quantities vary with the specific aggregate grading, moisture, how well it is compacted and how much is wasted. Order about 5 to 10% more than the estimate, and for structural work follow a specified mix design rather than a nominal ratio.
A 50 kg bag, which is the common size in much of the world. The US typically uses a 94 lb (about 42.6 kg) bag, and some markets use 40 kg, so adjust the bag count if yours differs. The cement mass in kilograms is shown so you can divide by your actual bag size.
Concrete includes coarse aggregate (gravel or stone) and is used for slabs, footings and structures. Mortar is just cement and sand, used to bond bricks and blocks or to render. The calculator uses a three-part ratio and higher bulking for concrete, and a two-part ratio for mortar.
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