Mortar Calculator
Find how much mortar a brick or block wall needs from the joint size, then the cement and sand bags for your mix. Advanced adds more walls, double leaf, lime, your own densities and cost.
Typical door about 0.9 × 2.1 m (3 × 7 ft), window about 1.2 × 1.2 m (4 × 4 ft).
Typical sizes. Check yours: they vary by maker and country.
Typical: 10 mm, or ⅜ in in the US.
Sizes vary by maker and country. Changing a size switches to "My own size".
Rough rule: 10–20% for spills, droppings and mortar that goes hard.
Common ratios only: 1:3 strong, 1:4 general, 1:5–1:6 for walls above ground. Check your local code or the maker.
Typical: an 80 lb (36 kg) bag of mortar mix makes about 0.67 cu ft (19 L). Check your bag.
Typical: dry mix ≈ 1.33 × wet mortar, loose cement ≈ 1440 kg/m³, dry sand ≈ 1600 kg/m³, hydrated lime ≈ 600 kg/m³.
How your mortar is worked out
Each brick plus its joint takes up a box. The mortar is the box less the brick. Add up every brick, add waste, then split the dry mix into cement and sand.
- 1
Mortar per brick
225 × 75 × 102.5− 215 × 65 × 102.5= 0.000297 m³ each
- 2
Bricks in the wall
10 m² × 59.259= 592.6 bricks
- 3
Mortar, plus waste
592.6 × 0.000297= 0.176 m³× 1.15 = 0.203 m³
- 4
Cement and sand
0.269 m³ dry (× 1.33)4 × 25 kg cement14 × 25 kg sand
Read more: the formula, a worked example, mix ratios and tips
Each brick or block, with half a joint on every side, takes up a box that is its length plus one joint, by its height plus one joint, by its depth. The mortar for that brick is the box less the brick. Count the bricks in the wall, multiply, and add some waste. Mortar shrinks as the water fills the gaps between the grains, so the dry cement and sand take up about a third more than the wet mortar.
The formula
mortar per brick = (length + joint) × (height + joint) × depth − length × height × depth
bricks = wall area less doors and windows ÷ ((length + joint) × (height + joint)) × leaves
wet mortar = bricks × mortar per brick (+ collar joint area × joint for a double leaf) × (1 + waste % ÷ 100)
dry mix = wet mortar × 1.33
cement = dry mix × 1 ÷ (1 + lime parts + sand parts) × 1440 kg/m³
sand = dry mix × sand parts ÷ (1 + lime parts + sand parts) × 1600 kg/m³
bags = mass ÷ bag size, rounded up · ready-mixed bags = wet mortar ÷ what one bag makes, rounded up
Worked example
A wall 5 m long and 2 m high is 10 m². A 215 × 102.5 × 65 mm brick with 10 mm joints takes up 0.225 × 0.075 = 0.016875 m² of the face, so there are 1 ÷ 0.016875 = 59.259 bricks per m² and 10 × 59.259 = 592.6 bricks in the wall (593 rounded up).
Each brick's box is 0.225 × 0.075 × 0.1025 = 0.00172969 m³ and the brick is 0.215 × 0.065 × 0.1025 = 0.00143244 m³, so its mortar is 0.00029725 m³. 592.59 × 0.00029725 = 0.17615 m³, and with 15% waste 0.17615 × 1.15 = 0.2026 m³ of wet mortar.
The dry mix is 0.2026 × 1.33 = 0.2694 m³. In a 1:4 mix there are 5 parts: cement is 0.2694 ÷ 5 = 0.05388 m³ × 1440 = 77.59 kg, which is 3.10 bags, so 4 bags of 25 kg. Sand is 0.2694 × 4 ÷ 5 = 0.2155 m³ × 1600 = 344.9 kg, which is 13.79 bags, so 14 bags of 25 kg.
Mortar per 1000 units (typical sizes, full joints, no waste)
| Unit and joint (typical) | Wet mortar |
|---|---|
| Brick 215 × 102.5 × 65 mm, 10 mm | 0.297 m³ (10.5 cu ft) |
| US modular brick 7⅝ × 3⅝ × 2¼ in, ⅜ in | 8.06 cu ft (0.228 m³) |
| Block 440 × 215 × 100 mm, 10 mm | 0.665 m³ (23.5 cu ft) |
| Block 8 × 8 × 16 in (7⅝ × 7⅝ × 15⅝ actual), ⅜ in | 39.1 cu ft (1.107 m³) |
Common mix ratios
| Cement : sand | Typical use |
|---|---|
| 1:3 | Strong: below ground, retaining walls, heavy loads |
| 1:4 | General masonry, outside walls in exposed places |
| 1:5 | General walls above ground |
| 1:6 (or 1:1:6 with lime) | Inside walls, softer bricks, general blockwork |
These ratios are common examples, not rules. Building codes and standards (for example mortar types M, S, N and O in the US, or designations in Europe) and the brick or block maker may set what you must use. The 1.33 dry-volume factor, the 15% waste and the densities (cement 1440, sand 1600, lime about 600 kg/m³) are rough rules of thumb, checked 13 October 2026. The maths assumes solid units with every joint full. Frogs laid up, holes or a fuller head joint take more. Face-shell bedding on hollow blocks takes less.
Tips
- Mix only what you can use in about two hours, and keep cement bags dry and off the ground.
- Keep the joint size the same across the wall: a 12 mm joint instead of 10 mm on a 215 × 65 mm brick uses about a sixth more mortar.
- Use the same batch of sand for a whole wall so the mortar colour matches.
Common questions
How much mortar do I need for 1000 bricks?
For a 215 × 102.5 × 65 mm brick with 10 mm joints, each brick takes 225 × 75 × 102.5 mm with its joint, and the brick itself is 215 × 65 × 102.5 mm. The difference, 0.00029725 m³, is its mortar. 1000 bricks need 0.297 m³ of wet mortar, or about 0.34 m³ with 15% for waste (typical).
How much cement and sand for mortar?
Take the wet mortar volume and multiply by about 1.33 to get the dry mix (a common rule of thumb). Split it by the ratio: in a 1:4 mix, cement is 1 part in 5 and sand is 4 parts in 5. Cement weighs about 1440 kg per m³ and dry sand about 1600 kg per m³ (typical). Divide by your bag size and round up.
What mortar mix ratio should I use?
Common ratios are 1:3 (strong, for below-ground or heavily loaded work), 1:4 (general masonry), and 1:5 or 1:6 (general walls above ground, often with lime or plasticiser). These are typical only. Your local building code, the engineer or the brick maker may set a different mix or a mortar type (M, S, N, O in the US).
How many bags of mortar mix for a block wall?
An 8 × 8 × 16 in block with ⅜ in joints uses about 67.6 cu in of mortar by geometry when the joints are full width. An 80 lb bag of ready mix makes about 0.67 cu ft (typical), so 100 blocks need about 3.9 cu ft, or about 7 bags with 15% waste (4.5 cu ft ÷ 0.67). Many blocks are laid with face-shell bedding, which uses less.
Why add 15% waste to mortar?
Some mortar always drops off the trowel, goes hard in the tub, or fills frogs and gaps. 10–20% extra is a common rough allowance. Use more for small jobs or first-time work, and less for skilled bricklayers on long straight walls.
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