One 80 lb bag of premixed mortar lays about 13 concrete blocks or 37 bricks, according to Quikrete's data sheets for Mason Mix and Mortar Mix. A 20 ft block wall 4 ft high holds 90 blocks, so it takes 8 bags once you add 15% for waste; the same wall in modular brick holds 540 bricks and takes 17 bags. If you mix your own Type S, that block wall needs 3 bags of portland cement, 1 bag of lime and about 10 cu ft of sand.
How the mortar is calculated
Mortar is estimated from the number of units you lay, because that is how manufacturers and the masonry trade publish it. The calculator first turns a wall into units (0.889 sq ft of wall per 8 × 16 in block, BIA's bricks per square foot for brick), then divides by what one bag or one batch lays:
bags = units laid × (1 + mortar waste) ÷ units per bag
Block is laid on face-shell bedding (mortar on the two face shells only), so NCMA says the mortar per block does not depend on its width: a 12 in block takes about the same mortar as an 8 in one. Brick larger than modular takes more: the count is scaled by BIA's mortar per 1000 bricks, 8.1 cu ft for modular against 14.2 cu ft for king brick at a 3/8 in joint.
Worked example: a 20 × 4 ft block wall
The calculator opens on this wall with 80 lb Quikrete mix:
- 20 ft × 4 ft = 80 sq ft, and 80 ÷ 0.889 = 90 blocks.
- 90 × 1.15 ÷ 13 blocks per bag = 7.96, so 8 bags (640 lb of dry mix).
- Mixing your own Type S instead: 90 ÷ 46 blocks per batch × 1.15 = 2.25 batches, which is 3 bags of portland cement, 2.25 × ½ = 1.1 cu ft of lime (1 bag of 50 lb), and 2.25 × 4½ = 10.1 cu ft of sand, about 0.4 tons.
How many blocks or bricks per bag of mortar
What each 80 lb bag lays, as printed by the maker (no waste included):
| Mortar | Bag | Blocks (8 × 8 × 16 in) | Standard bricks |
|---|---|---|---|
| Quikrete Mason Mix (Type S) or Mortar Mix (Type N) | 80 lb | 13 | 37 |
| Sakrete Mortar Mix Type S | 80 lb | 12 | 35 |
| Sakrete Mortar Mix Type S | 60 lb | 9 | 26 |
| Sakrete Mortar Mix Type S | 40 lb | 6 | 18 |
| Any preblended mortar, NCMA field average | 80 lb | 16 | 50 |
The NCMA figure (TEK 04-02A, Table 2) comes from experienced masons on real jobs; the bag figures are what the manufacturer stands behind. Picking Sakrete for the example wall gives 9 bags, the NCMA average 7. Buy by the maker's figure and return unopened bags.
Mortar for a brick wall
Switch to Brick. For the same 80 sq ft in modular brick, BIA Technical Note 10 gives 6.75 bricks per sq ft: 540 bricks, 17 bags of Quikrete mix. Mixed on site as Type S, 540 bricks lay at 225 per batch: 2.76 batches, 3 bags of cement, 2 bags of lime and 12.4 cu ft of sand. For the brick count itself, with waste, patio, fire pit and column layouts, use the brick calculator.
Type N, S, M or O
The four ASTM C270 types differ in strength. The Brick Industry Association's selection table (Technical Note 8B) is the simplest guide:
- Type N: the general-purpose mortar for above-grade veneer, non-loadbearing walls, chimneys and interior walls.
- Type S: for loadbearing and reinforced walls above grade, and the usual alternate to M below grade. Masons often use S and N interchangeably where strength allows.
- Type M: for foundations and retaining walls at or below grade.
- Type O: low strength, for interior partitions and repointing old soft brick.
Mixing your own mortar
The site-mixed recipes follow NCMA TEK 04-02A, Table 2, and sit inside the IRC's proportion table (R606.2.8): per 1 part portland cement, Type M takes ¼ part hydrated lime and 3¾ parts sand, Type S ½ and 4½, Type N 1 and 6, Type O 2 and 9. One batch starts with one 94 lb bag (1 cu ft) of portland cement and lays 38, 46, 62 or 93 blocks, or 187, 225, 300 or 450 brick-sized units. A 50 lb bag of hydrated lime is about 1¼ cu ft, and damp loose sand weighs about 80 lb per cu ft, so a ton of sand is 25 cu ft.
Why add 15% waste
BIA recommends adding 15 to 25% to the net mortar quantity for droppings, mortar left in the pan and batches that stiffen before they are used. The calculator starts at 15%. Raise it for a first project, hot and windy days, or a lot of cutting around openings.
What to work out next
- The block count, bond beam, core fill and rebar: the cinder block calculator.
- Bags of concrete for footings or core fill: the concrete bag calculator.
- Rebar for the footing or the wall: the rebar calculator.
- All block, brick and concrete tools: concrete and masonry calculators.