Mortar quantity is driven by how much joint volume a wall has, which depends on the unit size, the joint thickness, and the wall area. This calculator estimates that volume, adds a waste allowance, and converts it into bags of pre-mixed mortar or into separate Portland cement and mason’s sand quantities at the ratio for your chosen mortar type.
Choosing the right mortar type
Picking the correct type is as important as estimating the quantity. ASTM classifies mortar into four main types for masonry:
| Type | Strength profile | Typical use |
|---|---|---|
| N | Medium strength, most flexible | General above-grade exterior walls, veneers, chimneys |
| S | High strength, moderate flexibility | Below-grade walls, retaining walls, at/below grade |
| M | Highest strength, least flexible | Foundations, walks, sewers, heavy load-bearing |
| O | Low strength, very flexible | Interior non-load-bearing, soft historic brick |
Type N is the right choice for most residential above-grade brick work. It bonds well, accommodates slight movement from temperature cycling, and is easier to work with. Type S is specified where structural loads are higher or moisture exposure is significant. Type M is for foundations and work below grade where compressive strength matters most — but its rigidity makes it a poor choice where the masonry or substrate moves seasonally, since it cracks rather than flexing.
How it works
The tool starts from an empirical mortar-per-area figure that already accounts for the joint geometry of brick versus block, then scales by area and waste:
mortar volume (cu ft) = area_sqft × mortar_per_100sqft / 100 × (1 + waste)
premix bags = ceil(volume / yield_per_bag)For a site mix, the volume is split by the type’s cement-to-sand parts ratio:
- Type N: roughly 1 part cement to 3 parts sand
- Type S: roughly 1 part cement to 2.5 parts sand
- Type M: roughly 1 part cement to 2.25 parts sand
cement volume = volume × (1 / (1 + sandParts)) then ÷ Portland-bag yield
sand volume = volume × (sandParts / (1 + sandParts))Worked example: 160 sq ft brick wall
A single-wythe brick wall of 160 square feet with standard 3/8 inch joints:
- Mortar per 100 sq ft: approximately
7 cubic feet - Base volume:
160 × 7 / 100 = 11.2 cu ft - With 10% waste:
11.2 × 1.10 ≈ 12.3 cu ft - Pre-mixed 80 lb bags (approx. 0.9 cu ft yield each): about 14 bags
For a Type N site mix from the same volume:
- Cement:
12.3 × (1/4) = 3.1 cu ft→ roughly 3 bags of 94 lb Portland - Sand:
12.3 × (3/4) = 9.2 cu ft
Practical tips for mortar work
Batch size: mix only what you can place in roughly 90 minutes. Mortar that begins to stiffen must be discarded — never re-temper it by adding water, which destroys the bond strength.
Joint consistency: use a mortar board and keep it loaded with fresh mortar at the right working consistency. Mortar that drags rather than flows smoothly is getting stiff.
Weather: do not lay masonry if temperatures will fall below freezing before the mortar cures (usually 28 days to full strength). Cold mortar loses strength permanently. In hot weather, dampen the brick or block before laying to slow moisture absorption, which can pull water out of the mortar too quickly and weaken the bond.
Pointing and repointing: for repairs, rake existing joints to at least 3/4 inch depth before applying new mortar, and match the existing mortar type as closely as possible. Using a harder modern type (e.g., Type S or M) in old soft-brick walls can cause the bricks themselves to crack, since the brick and mortar need to move together.