Masonry Mortar Calculator
Start with the masonry units that will actually be installed, then use coverage for the matching unit, joint, bedding method, and mortar product.
- Installed masonry units
- 130
- Fractional bags
- 11
- Whole bags to buy
- 11
- Coverage headroom
- 0 units
Use installed units—not masonry units already increased for purchase waste. Coverage must match the unit geometry and joint method.
Show calculation
130 units × (1 + 10%) ÷ 13 units/bag = 11 bagsTransparent method and editable product assumptions. Verify current labels and project requirements.
How this calculator works
Enter installed masonry units, not the block or brick purchase quantity after its own waste. This prevents the masonry allowance from being carried into the mortar estimate and then increased again.
Divide installed units plus a separate mortar allowance by the product’s published units-per-bag coverage. QUIKRETE Mortar Mix 1102 states up to 13 standard 8 × 8 × 16-inch blocks or 37 standard bricks per 80 lb bag under its stated conditions.
Coverage changes with unit geometry, joint thickness, full-bed versus face-shell bedding, technique, and product. Hollow CMU cores are not mortar joints, so the calculator does not subtract block exterior volume from wall volume.
Formula
Bags = ceil[installed masonry units × (1 + mortar waste) ÷ product units per bag]The live substitution appears with your result.Control example: 130 standard blocks
At 13 installed blocks per 80 lb bag, 130 blocks require exactly 10 bags before waste.
With 10% mortar waste: ceil(130 × 1.10 ÷ 13) = 11 bags.
Assumptions and limits
- Coverage matches the masonry unit and bedding method.
- Installed units exclude purchase-only spare blocks or bricks.
- Mortar waste is applied once.
- This estimates bags, not bond, wall strength, reinforcement, or code compliance.
Common measuring mistakes
- Feeding a block count that already includes purchase waste into the mortar form.
- Treating hollow block core space as mortar volume.
- Moving a units-per-bag preset between different block sizes or bedding methods.
Sources
Product-specific values remain editable. These sources support the method and stated examples; they are not a universal substitute for your supplier’s current label.
- QUIKRETE Mortar Mix 1102 data sheet Up to 37 standard bricks or 13 standard 8 × 8 × 16-inch blocks per 80 lb bag.
- QUIKRETE Mortar Calculator States a ⅜-inch mortar joint and excludes waste.
Questions people ask
Should I use ordered blocks or installed blocks?
Use installed units. Block or brick purchasing waste should not automatically increase mortar a second time.
Why not calculate mortar as wall volume minus block volume?
That would incorrectly treat hollow cores as mortar. Mortar belongs in bed and head joints according to the bedding method.
Can I use 13 blocks per bag for every CMU?
No. It is a product- and geometry-specific example. Replace it when unit size, joint, bedding, or mortar changes.