Cement Mortar Calculator
Work out how much cement and sand a mortar mix needs for brickwork or blockwork, based on the wall volume and your ratio.
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Formula and method
Wall volume gives the wet mortar volume. A dry-to-wet factor converts this to dry material, which is then split between cement and sand according to the mix ratio. Density converts volume to mass.
Mix ratio decides cement, not the volume
A 1:3 mix is one part cement to three parts sand by volume, so the cement content of a cubic metre is fixed by the ratio rather than by the job. Going from 1:4 to 1:3 uses roughly a third more cement for the same volume, and on a bricklaying job that is several bags per cubic metre.
Stronger is not better for mortar. A mix stronger than the masonry it bonds will crack at the joint instead of the block, and the repair is then in the wall rather than in the mortar. Use the ratio specified for the unit, not the one that feels safest.
Dry volume, bulking and the sand you buy
Sand bulks when damp: a tonne of dry sand becomes a larger volume when wet, and buying by volume from a supplier who measures in loose cubic metres means you can receive less material than you think. Mix ratios are quoted by volume of dry materials, so the bulking factor of about 20 to 30 % has to be in the order.
Water is about half the cement weight in a workable mortar and is never counted as a purchase. Adding water on site to revive a stiff mix weakens it; the correct fix is to mix a smaller batch.
Where mortar goes besides the joints
Bedding the first course, filling blocks, pointing and repair all consume mortar that never appears in the joint calculation. A bricklaying job typically needs 10 to 15 % more than the wall volume suggests, and rendering needs its own quantity at a different ratio.
Order sand in the largest practical delivery and keep it covered. Wet sand from a tarpaulin edge is fine; sand that has sat in the rain for a week and set in the heap is not, and the cement you save by buying in bulk disappears in wasted batches.
How to measure the inputs
- Measure the wall length and height and enter the wall thickness.
- Deduct large openings to avoid over-ordering.
- Confirm the mix ratio from the specification or your engineer.
Worked example
Wall length 16.4 ft; Wall height 9.84 ft; Wall count 1; Wall thickness 7.87 in; Cement ratio 1; Sand ratio 3; Density (optional) 1,800 kg/m³; Waste 10 % → Total mortar mass: 26,125.44 lb
Reference data
| Cement : sand | Cement, kg | Sand, kg | Water, l |
|---|---|---|---|
| 1 : 3 | 450 | 1,350 | 230 |
| 1 : 4 | 350 | 1,400 | 210 |
| 1 : 5 | 300 | 1,450 | 200 |
Proportions are by volume before mixing; water is adjusted on site to the required workability.
Practical tips
- Mix only what you can use within about an hour of adding water.
- Store cement off the floor and use older bags first.
- Measure sand and cement by volume with the same container for consistency.
Sources
- ГОСТ 28013-98 — Растворы строительные
Checked and updated October 22, 2026