Masonry mortar guide
Start with wall dimensions and openings. The default 60 × 20 × 10 cm blocks, 10 mm joints and 15 L mixed mortar per bag are illustrative; adjust to the chosen products.
Back to calculator ↑Measure and prepare
Measure the wall, then count equal-size doors and windows or enter their known combined area to get net wall area. Use the unit face dimensions, wall depth and specified joint. The example uses a 0.6 × 0.2 m unit, 0.1 m wall depth and 0.01 m joints.
Use the same net wall and unit face measurements as the block estimate. Add wall depth so joint area becomes wet mortar volume. Confirm that the selected system uses full-depth bed and head joints. Thin-bed adhesive or unusual hollow-unit details need manufacturer consumption data instead of this geometric approximation.
How the estimate works
Joint fraction is 1 minus unit face area divided by face-plus-joints module area. Multiply by wall area and depth for wet mortar volume, add allowance, then divide by wet yield per bag.
The example module is 0.61 × 0.21 = 0.1281 m², while the unit face is 0.12 m². Joint fraction is 1 − 0.12 ÷ 0.1281 = 6.32%. A net 10 m² wall at 0.1 m depth needs about 63.2 L in joints. Adding 15% gives 72.7 L; divided by 15 L wet yield per bag is 4.85, rounded to five bags.
Check the order
Check wet mixed yield and unit compatibility on the selected bag; thin-bed adhesive and render have different rates.
Use the selected bag’s wet mortar yield; do not treat dry kilograms as wet litres. Match mortar type to the masonry unit and exposure conditions. Estimate render and core fill separately. For a large order, confirm bag size, production date and dry storage conditions with the supplier.
Limits of the estimate
The uniform-joint model excludes core fill, ties, lintels and render.
The formula assumes uniform, full-depth joints throughout and does not model course details at corners. Dropped material, gap filling and cut units alter site consumption. The editable 15% allowance is a planning margin, not a guaranteed product yield or a substitute for a trial section. Do not mix more mortar than the crew can place within the product’s working time. Material that has begun to set must be discarded and raises actual bag consumption.
Common questions
Can I use this for AAC adhesive?
Not directly; use the chosen adhesive’s stated coverage.
Is bag yield its dry weight?
No. Enter wet mixed mortar volume in litres.
Is render included?
No. Calculate render separately from thickness and coverage.
Sources and calculation guidance
Check these against your chosen product’s label and instructions.