Mortar Calculator
Works out mortar from a brick or block count, or from a volume you already have. Gives the cement bags and sand for the mix ratio you pick.
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The formula
dry volume = wet mortar × 1.3 cement = dry volume ÷ (ratio + 1) × 1,440 kg/m³ sand = dry volume × ratio ÷ (ratio + 1)
The 1.3 factor is why mixing by the book still leaves you short: loose sand and cement pack down and lose volume when wetted, so a cubic metre of finished mortar takes about 1.3 cubic metres of dry ingredients.
What to watch out for
The mix ratio is a real decision, not a formality:
- 1:3 — strong. Engineering brick, below damp course, exposed work.
- 1:4 — the general-purpose brickwork mix.
- 1:5 to 1:6 — softer, for blockwork and older soft brick.
Stronger is not better. Mortar should be weaker than the units it beds, so that movement cracks the joints rather than the bricks — a cracked joint is repointed, a cracked brick is not. This is why hard cement mortar on an old soft-brick wall does so much damage.
Frequently Asked Questions
How much mortar do I need for 1,000 bricks?
About 0.41 m³ with a 10% waste allowance — roughly 7 bags of 25 kg cement and 0.68 tonnes of sand at a 1:4 mix.
What is the right mortar mix for bricklaying?
1:4 cement to sand for general brickwork. Use 1:3 below damp course or for engineering brick, and 1:5 or 1:6 for blockwork and soft older brick.
How many bags of cement per cubic metre of mortar?
About 15 bags of 25 kg at 1:4, or 13 at 1:5. The dry ingredients add up to roughly 1.3 m³ for every cubic metre of finished mortar.