Mortar calculator
We work the mortar out from the real volume of the joints.
Your inputs
Your inputs are processed on your device and are not sent to a server.
Example loaded. You can change any value.
There is no figure yet: nothing is calculated until you ask for it.
- Enter your measurements.
- Check the units and the assumptions.
- Press Calculate, or load the example.
Rather see a worked case? Press “Load example” and change any value afterwards.
Next step
The same wall tells you how many units to buy, breakage included.
Where each number comes from Conversion constants are exact; densities and coverage rates come from cited sources; everything else is an assumption you can change. Methodology · Sources and updates
How to use it
- Enter the area of wall you are building.
- Set the real unit size and the wall thickness.
- Adjust the joint: 10 mm (3/8 in) is standard for brick and block.
- If you use bagged mortar, enter the litres each bag yields.
How it is calculated
The mortar in a wall is, literally, the space the units leave. So the calculation starts from the share of the wall that is joint:
With an 8 x 2.25 in brick and a 3/8 in joint, the module is 8.375 x 2.625 in. The brick occupies 18 of the 22 square inches of the module, so the joint is about 18 % of the wall. That percentage, times the thickness, gives the mortar volume.
Default waste is 15 %, higher than for other materials, and rightly so: mortar drops, dries in the bucket, stays on the trowel and goes off if you are slow. Nobody lays 100 % of what they mix.
Worked example
A 108 sq ft wall in 8 x 2.25 in brick, 3/8 in joint, 4 in thick, with 15 % waste:
- Module: 8.375 x 2.625 = 21.98 sq in
- Joint share: 1 - 18 / 21.98 = 18.1 %
- Volume: 10 m² x 0.102 m x 0.181 = 0.185 m³
- With waste: 212 litres (7.5 cubic feet)
Good to know
- Thicker joint, more mortar. Going from 10 to 15 mm raises consumption by roughly half.
- Hollow block is misleading. If the block has cores and you fill them, the figure jumps: that is grout or fill concrete, not bedding mortar.
- Mix what you will lay. Mortar has a limited working time. Mixing too much is throwing it away.
- Bedding and rendering are different. This calculator is for laying units. For rendering or plastering, use the plaster calculator.
Frequently asked questions
How much mortar per square metre of brickwork?
With a 24 x 11.5 cm brick, a 10 mm joint and a 11.5 cm thick wall, about 13.4 litres per square metre before waste, or 15.5 litres with the usual 15 %.
Why is the mortar waste allowance so high?
Because it is lost in many ways at once: off the trowel, stuck to the bucket and barrow, and whatever is left at the end of the day has gone off. 15 % is realistic, not pessimistic.
How many bags of mortar do I need?
It depends on the yield printed on the bag, given in litres of wet mortar. If a bag yields 20 litres and you need 212, that is 11 bags. Enter your bag's yield in the field provided.
Does this work for concrete block?
Yes. Change the unit size and the wall thickness. With a 16 x 8 in block the joint share drops noticeably, because there are far fewer joints per square metre.