How to Calculate Sand and Cement for Mortar
Whether you're building a new garden wall, laying a blockwork foundation, or repointing an old brick facade, mixing the right amount of mortar is essential. Estimating incorrectly can lead to expensive emergency trips to the builder's merchant or messy leftover materials.
Our Mortar Calculator helps you accurately estimate the exact number of 25kg cement bags and building sand (in 25kg or bulk bags) needed for your masonry project. It automatically factors in the standard 10mm joint thickness and a sensible waste margin.
Common Mortar Mix Ratios
Mortar is a mix of building sand, cement, and water (often with a plasticiser). The ratio you choose determines the workability and final compressive strength of the mortar. The most common UK mix ratios by volume are:
- 1:4 (1 part cement to 4 parts sand): The standard general-purpose mix for most brickwork and blockwork. Offers good strength and weather resistance.
- 1:3 (Strong mix): Used for exposed areas like chimney stacks or below damp-proof courses where extra durability is needed.
- 1:5 or 1:6 (Weaker mix): Typically used for repointing softer, older bricks where the mortar needs to be more porous than the brick itself.
What kind of Sand should I use?
For laying bricks and blocks, always use Building Sand (also known as soft sand). Building sand has smooth, rounded grains that make the mortar "fatty" and easy to spread with a trowel. Never use sharp sand for bricklaying mortar, as it results in a rough, brittle mix that is difficult to work with. (Sharp sand is reserved for floor screeds and concrete).
Factoring in Waste
When mixing mortar, a lot is dropped from the trowel ("snots") or hardens on the mixing board before it can be used. Our calculator builds in an industry-standard 10% waste allowance to ensure you never run short mid-course.