Mortar quantities are worked out from the joints, not from the wall, and the two lead to very different answers depending on what you are actually doing. Building a wall from new means filling every joint through the full depth of the masonry. Repointing an existing one means refilling only the oute...
Module 225 mm × 75 mm · 59.26 units per m² · 17.61 litres of mortar per m²
MORTAR REQUIRED — NEW WORK
0.507 m³
24.00 m² · including 20% waste · about 6 mixer loads
CEMENT
5 bags
LIME
2 bags
SAND
0.495 m³
Net area
24.00 m²
Units per m²
59.26
Mortar per m²
17.61 litres
Mortar before waste
0.4228 m³
With 20% waste
0.5073 m³
Dry materials
0.6595 m³
Cement
118.7 kg / 5 bags
Lime
49.5 kg / 2 bags
Sand
0.495 m³ (791 kg)
Water, roughly
92 litres
MIXING AND LAYING
Order 5 bags of cement, 2 bags of lime and 0.495 m³ of soft sand.
Mix in batches of about 90 litres — roughly 6 loads for this wall — and only as much as you can lay before it stiffens.
Keep the joints consistent at 10 mm bed and 10 mm perpend. The coverage figure only holds if the joints do.
Tool the joints while the mortar is thumbprint-hard. Left until set, they have to be ground out and pointed again.
THE JOINTS
Bed and perpend are not always the same. Here they are both 10 mm, but they are separate inputs because they need not be — and on US modular brick they are genuinely different, which is why that unit's published coverage cannot be reproduced with a single joint size.
Lime makes the mix workable and lets fine cracks close themselves over time. It also makes the mortar weaker than the units it joins, which is what you want — movement should be taken up in joints you can repoint rather than in bricks you cannot.
Live calculation · updates as you type
Choose new work or repointing first — it changes the calculation completely, not just a number. New work fills the joint through the full depth; repointing refills only the raked band.
Enter the wall area as length and height with any openings deducted, then pick the unit. Selecting a unit brings its correct bed and perpend joints with it, which matters on US modular brick where the two differ.
For repointing, set the rake depth. The usual guide is at least twice the joint width — around 20 mm for a 10 mm joint — and the calculator warns you if it is too shallow to hold.
Open mix and materials to set the cement, lime and sand proportions. Set lime to zero for a plain cement mortar; the presets cover the common cases including a pure lime mix for heritage work.
| Unit | Module | Per m² | Bedding | Repoint at 20 mm |
|---|---|---|---|---|
| UK brick 215 × 102.5 × 65 mm | 225 × 75 mm | 59.26 | 17.6 L | 3.4 L (20%) |
| UK block 440 × 215 × 100 mm | 450 × 225 mm | 9.88 | 6.6 L | 1.3 L (20%) |
| UK block 440 × 215 × 140 mm | 450 × 225 mm | 9.88 | 9.2 L | 1.3 L (14%) |
| Block 390 × 190 × 190 mm | 400 × 200 mm | 12.50 | 14.0 L | 1.5 L (11%) |
| US modular brick (4 × 2⅔ × 8) | 8.00 × 2.67 in | 72.66 | 18.0 L | 3.9 L (22%) |
| US queen brick | 8.00 × 3.13 in | 62.00 | 11.3 L | 3.2 L (29%) |
| US CMU 8 × 8 × 16 in | 16.00 × 8.00 in | 12.11 | 13.4 L | 1.4 L (10%) |
Figures are geometric, before any wastage allowance. Note the last column: repointing takes somewhere between a sixth and a quarter of the mortar a new wall does, because only the outer band of each joint is being replaced rather than the full depth.
Last updated: July 29, 2026 · Formula verified · Eagle-eyed accuracy for every calculation.