Concrete & Masonry
Mortar Calculator
Bags of mortar for block, brick and stone work, matched to mortar type and joint size.
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Results
Adjust the inputs to see your result.
About this calculator
Mortar estimates are usually given per 100 blocks or per 1,000 bricks, which makes them useless mid-project. This calculator starts from your wall area and unit size, and returns bags by type — N for above-grade walls, S for below-grade and load-bearing work.
What this number means
Mortar is sold by the bag but consumed by the joint, and the only honest conversions are the yield tables: how many units one bag actually lays. Those yields are stable across brands for pre-mix — about 30 standard blocks or 110 modular bricks per 80 lb bag — because joint dimensions, not brand chemistry, set the volume.
The result also shows the mixed volume your bags represent (about 0.88 cu ft per 80 lb bag), which is the number to compare against site-mixed mortar if you are deciding between pre-mix bags and a cement-lime-sand order.
The formula
- Yield per 80 lb bag: ~30 standard blocks (36 half-high, 42 half blocks); ~110 modular bricks (100 queen, 88 king)
- 60 lb bags yield 0.75 × the 80 lb figure
- Bags = Units ÷ yield per bag, rounded up
- Mixed mortar volume ≈ Bags × 0.88 cu ft (80 lb) or 0.66 cu ft (60 lb)
Mortar type changes the mix proportions and strength, not the volume — the bag count is the same for N, S, M and O.
Worked example
500 standard blocks, type S, 80 lb bags.
- Yield = 30 blocks per bag → 500 ÷ 30 = 16.7 → 17 bags
- Mixed volume ≈ 17 × 0.88 ≈ 15 cu ft of mortar
- The same 500 units in modular brick would take only ceil(500 ÷ 110) = 5 bags — brick joints are far smaller than block joints
Assumptions and limitations
- Yields assume 3/8 in joints, struck flush. Head joints left partially empty (a common shortcut) reduce use but weaken the wall — the estimate assumes the job done properly.
- Yields are for pre-mixed bagged mortar. Site-mixed mortar is ordered as cement + lime + sand; as a rough conversion, 15 cu ft of mixed mortar ≈ 6 bags of masonry cement plus about 0.55 cu yd of sand, but proportions vary by type — confirm with your supplier.
- Repointing old work uses mortar differently (joints are raked out and refilled to depth) — these yields are for new laying.
- Coloured mortar and additives do not change volume yields.
Frequently asked questions
About 3.3 — so buy 4 bags of 80 lb pre-mix for standard 8×8×16 block, and you will use most of the fourth. The rate behind it is roughly 30 blocks per bag, which is the figure block manufacturers publish.
Compressive strength and intended use. Type M is strongest (foundations, retaining walls), S is the general structural choice (below grade, load-bearing), N is the standard for above-grade exterior and interior walls, and O is weak by design for repointing soft historic brick. The bag count is identical — pick the type for the job, not the quantity.
Joint volume. A block joint network carries roughly four times the mortar per unit because the units — and their joints — are far bigger. Per 80 lb bag you lay about 30 blocks but about 110 modular bricks.
About 0.88 cu ft once mixed with water. That figure lets you compare pre-mix against site-mixing: a cubic yard of mortar is roughly 31 × 80 lb bags' worth.
One or two, yes. Mortar is cheap, unopened bags keep for months if stored dry, and colour/brand consistency matters — finishing a wall with a different brand of pre-mix can show. The calculator rounds up already; a single spare bag on top is sensible for walls over a few hundred units.