Mortar Mix Calculator

Q: What is the best mortar mix ratio for bricks?

For general brickwork above ground, 1:5 or 1:4 cement to building sand is common. Use 1:3 below ground and 1:6 for internal walls.

Q: How much sand do I need for one bag of cement?

For a 1:4 mix, one 50 kg bag (about 0.035 m³) needs about 0.14 m³ of sand, roughly 220 kg. On site, measure 1 bucket of cement to 4 buckets of sand.

Q: Why is the dry volume factor 1.33?

Loose sand contains air voids that the cement paste fills, so wet mortar is about 25% smaller than the dry materials.

Work out the cement, sand and water for any quantity of mortar. Choose the cement : sand ratio that suits your job, from strong 1 : 3 mortar for below-ground work to 1 : 6 for general brickwork, and get the number of bags to buy.

Ratios 1:3 to 1:8Cement, sand & waterMetric & imperialLast updated: November 2, 2026

Calculate mortar materials

Wet mortar volume

m³

Not sure? Use the brick or block calculator first.

Cement : sand ratio

Cement bag

Waste allowance

Mortar calculation formula

Sand has about 25–33% air between its grains, and cement fills much of that space when water is added. So you need more dry material than the wet mortar you end up with. The standard factor is 1.33.

Dry volume

V_dry = V_wet × 1.33 × (1 + waste%)

Cement and sand

Cement (m³) = V_dry ÷ (1 + n) · Sand (m³) = V_dry × n ÷ (1 + n)

n is the sand part of a 1 : n mix. Cement weight = cement volume × 1,440 kg/m³. In imperial, one 94 lb bag of Portland cement is 1 ft³.

Water

Water ≈ cement weight × 0.6

Mortar is wetter than concrete; a water–cement ratio around 0.55–0.65 gives a workable, buttery mix. Add water gradually.

Which mortar ratio should I use?

Ratio	Strength	Typical use	Similar to
1 : 3	High	Below damp-proof course, retaining walls, chimneys, paving bedding	Type M / M12
1 : 4	Medium-high	Exposed external walls, copings, load-bearing brickwork	Type S / M6
1 : 5	Medium	General brick and blockwork above ground	Type N / M4
1 : 6	Medium-low	Internal walls, cement plaster on masonry	Type N / M2
1 : 8	Low	Light, non-load-bearing partitions	Type O

Comparisons with ASTM C270 types (M, S, N, O) and EN 998-2 classes are approximate; those standards use cement-lime mixes and strength tests rather than simple ratios.

Materials per 1 m³ of wet mortar

Ratio	Cement	50 kg bags	Sand
1 : 3	479 kg	9.6	1.00 m³
1 : 4	383 kg	7.7	1.06 m³
1 : 5	319 kg	6.4	1.11 m³
1 : 6	274 kg	5.5	1.14 m³
1 : 8	213 kg	4.3	1.18 m³

No waste included. Use dry, well-graded building (soft) sand for brickwork and sharp sand blends for paving and floor screeds.

Worked example: 0.5 m³ of 1 : 4 mortar

Dry volume = 0.5 × 1.33 × 1.10 = 0.7315 m³
Cement = 0.7315 ÷ 5 = 0.1463 m³ × 1,440 = 211 kg → 5 × 50 kg bags
Sand = 0.7315 × 4 ÷ 5 = 0.585 m³ (≈ 0.94 t)
Water ≈ 211 × 0.6 ≈ 127 litres

Frequently asked questions

What is the best mortar mix ratio for bricks?

For general brickwork above ground, 1 : 5 or 1 : 4 cement to building sand is common. Use 1 : 3 below ground or for retaining walls, and 1 : 6 for internal walls.

How much sand do I need for one bag of cement?

For a 1 : 4 mix, one 50 kg bag (about 0.035 m³) needs about 0.14 m³ of sand, roughly 220 kg of dry sand. On site it is easiest to measure by volume: 1 bucket of cement to 4 buckets of sand.

Why is the dry volume factor 1.33?

Loose sand contains air voids. When cement and water are added, the paste fills those voids, so the wet mortar is about 25% smaller than the dry materials. Multiplying by 1.33 compensates.

Brick Wall CalculatorBricks and mortar volume Concrete Block CalculatorBlocks and mortar Plaster CalculatorPlaster and render Sand CalculatorSand tonnage

Results are estimates. Follow your engineer’s or local code requirements for mortar strength in structural masonry.