Masonry Mortar Mix Calculator
Cement, sand and water for M5-M15 mortar by volume, with a batch sheet.
Inputs
Result
Formula
| Cement | M = reference by grade × volume |
| 42.5 class | reference × 0.88 |
| Sand | V = 1.02 × mortar volume (loose) |
| Water to add | W = 280 × V − moisture in sand |
| Strength | 70.7 mm cube at 28 days |
1 m³ of M7.5 with 32.5 class cement and 2% sand moisture: 220 kg cement (5 bags), 1.02 m³ of dry sand around 1479 kg and about 250 kg of added water — a ratio near 1 : 6.7.
FAQ
What does M7.5 mean?
A mean compressive strength of at least 7.5 MPa for 70.7 mm cubes cured 28 days. It is a mean, not a characteristic value, and the specimen is a 70.7 mm cube — not the 150 mm cube used for concrete. Mortar test results scatter far more than concrete.
Why deduct the water in the sand?
Sand at 2% moisture brings about 30 kg of water per cubic metre; adding the full 280 kg pushes the water-cement ratio over 10% high, costing 15-20% strength and increasing shrinkage. In the rainy season sand can reach 8%. Measure moisture each shift by drying or a rapid meter.
Is more cement always better in mortar?
No. Excess cement increases shrinkage and cracking, mismatches brick movement and costs more. The key property is workability — water retention and consistency — which lime putty or fly ash improve better than extra cement. The code sets a minimum cement content but also discourages over-strong mortar in masonry.
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Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.