Mortar calculator
Estimate 25 kg cement bags and building sand for brickwork, blockwork and pointing. Choose your mix ratio (1:3, 1:4, 1:5 or 1:6), add a wastage allowance and request a trade quote.
Mortar volume
0.3 m³
Cement (25 kg bags)
6
Building sand
0.63 t
Tip: these figures assume a standard 25 kg cement bag. Round up to whole bags and tonne bags when ordering.
How the mortar calculator works
Enter your wall area in square metres and the calculator converts it into litres of wet mortar, then into 25 kg cement bags and kilograms of building sand based on the mix ratio you select. The figures use the trade rule of thumb of roughly 1.5 kg of dry mortar per standard brick and 5 kg per 440 × 215 mm solid block.
Picking the right mortar mix
- 1:3 – strong, dense mortar for below-ground work, manholes and coping stones.
- 1:4 – general-purpose mix for external brickwork, load-bearing walls and chimney stacks.
- 1:5 – standard mix for internal blockwork and most above-ground bricklaying.
- 1:6 – weaker, more breathable mix for lime-friendly brick or softstone pointing.
Tips for an accurate order
Always add 10% wastage to cover board clean-down, dropped mortar and bed thickness variation. For pointing only, allow 5% extra. If you are using pre-mixed mortar or silicone pointing compounds, change the mix selector in the calculator to match the bag coverage on the pack. For brick matching or coloured mortar, call the trade counter before ordering.
Common projects
Quick reference quantities for the jobs we get asked about most. Enter your own measurements in the calculator above for an exact figure.
Single-skin brick wall
10 m² of single-skin brickwork needs roughly 25–30 kg of cement plus the matching sand.
100 mm block wall
15 m² of 100 mm blockwork needs roughly 10–12 bags of 25 kg cement.
Repointing
20 m² of repointing needs roughly 3–4 bags of cement depending on joint depth and width.
Garden wall
A 5 m × 1 m single-skin garden wall needs roughly 5–6 bags of 25 kg cement.
Frequently asked questions
- What mix ratio should I use for brickwork?
- A 1:5 cement-to-sand mix is standard for general above-ground brickwork. Use 1:4 below the damp-proof course or in exposed positions.
- How much sand do I need per bag of cement?
- For a 1:5 mix, combine one 25 kg bag of cement with roughly 125 kg (5 bags) of sharp sand.
- Should I add lime or plasticiser?
- Lime improves workability and breathability for older brickwork. A mortar plasticiser is a common alternative for modern masonry.
- When is a 1:6 mortar mix used?
- A 1:6 mix is weaker and more breathable. It suits internal blockwork, soft brick or stone repointing.
- How do I calculate mortar for blockwork?
- Enter the wall area, block size and joint thickness. The calculator converts this into litres of wet mortar and then into cement bags and sand.