Mortar Calculator

At 1:6, about 6 bags of cement and 1.14 m³ — roughly 40 cft — of sand. The wet volume of 1 m³ becomes 1.33 m³ of dry material, split one part cement to six parts sand. At 1:4 the same volume takes about 8 bags and 1.06 m³ of sand.

1:6 for ordinary brick and block masonry and internal plaster. 1:4 for external plaster, tile bedding and load-bearing or exposed brickwork. 1:3 for pointing, repairs and waterproofing work, where you need the strength on a small quantity. 1:8 only for non-structural filling. Richer is not simply better — a strong mix shrinks more as it cures and cracks along the joints.

Because dry cement and sand contain a lot of air. Once mixed and packed into a joint the material consolidates and loses about a third of its bulk, so the dry quantity you buy is about a third more than the finished mortar you end up with. Skipping this step is the reason a job that was measured correctly still runs short.

Roughly half the weight of the cement — about 25 litres for a 50 kg bag — but it depends on how damp the sand already is and on the weather. Extra water makes mortar easier to spread and measurably weaker, so add it in small amounts rather than making the mix comfortable.

Around 20–25% of the wall volume for standard brickwork with 10 mm joints, though it depends on the brick size and the joint thickness. If you are estimating brickwork rather than a known volume of mortar, the brick calculator works out both the bricks and the mortar from the wall dimensions.