How much mortar do I need?
Last reviewed 1 July 2026
Short answer
About 0.033 m³ of mortar per square metre of single-skin UK brickwork, which works out at roughly 0.55 m³ per 1,000 bricks. That needs around 0.9 tonnes of building sand and 175 kg of cement at a 1:5 mix — about seven bags of 25 kg cement per thousand bricks.
Work it out for your project with the brick wall calculator →
Where the mortar actually goes
Pure joint geometry accounts for less than you would think. In a square metre of half-brick UK work, the bed and perpend joints amount to about 0.0176 m³.
Filling the frog — the indent pressed into the top of most UK bricks — adds roughly another 0.0089 m³ per square metre. That is a third of the total, and it is why estimates based only on joint geometry come out about 40% short.
A site allowance of about 25% on top covers over-filled perpends, mortar dropped off the board and what stays in the mixer. Total: about 0.033 m³ per square metre.
mortar = joint volume + frog filling, plus about 25% site allowance
Mortar and materials by quantity
| Bricks | Wall area | Mortar | Building sand | Cement (25 kg bags) |
|---|---|---|---|---|
| 500 | 8.4 m² | 0.28 m³ | 0.45 t | 4 |
| 1,000 | 16.9 m² | 0.56 m³ | 0.90 t | 7 |
| 2,000 | 33.7 m² | 1.11 m³ | 1.78 t | 14 |
| 5,000 | 84.4 m² | 2.78 m³ | 4.45 t | 36 |
Sand at 1.6 tonnes per m³ of mortar, cement at 320 kg per m³ for a 1:5 mix.
Blockwork uses much less
A 440 × 215 mm block has far less joint length per square metre than bricks do, and no frog. Blockwork works out around 0.008–0.010 m³ per square metre — roughly a quarter of brickwork.
US hollow concrete blocks use less still, because they are bedded on their face shells only rather than across the full width of the unit. Only the two 1¼ in shells carry mortar, not the 7⅝ in wall thickness.
Choosing the mix
| Mix (cement:sand) | Cement per m³ | Use |
|---|---|---|
| 1:3 | 480 kg | Engineering brick, below DPC, very exposed work |
| 1:4 | 400 kg | Exposed walls, retaining work, chimneys |
| 1:5 | 320 kg | General purpose — most walls above DPC |
| 1:6 | 270 kg | Sheltered and internal work, soft bricks |
A mortar stronger than the brick is a mistake. It forces cracks through the units rather than the joints, where they cannot be repaired.
Important: Use building sand, not sharp sand
Practical notes
- Mix in batches you can lay within about two hours. Retempering mortar that has started to set ruins the strength.
- Use a proprietary plasticiser or lime for workability. Washing-up liquid entrains uncontrolled air and weakens the mortar.
- Keep the mix consistent between batches or the joint colour will band across the wall — very obvious once it dries.
- Order sand in bulk bags rather than handy bags above about half a tonne. It is far cheaper and the bag can sit next to the mixer.
Safety notice: Material planning only