Enter the number of blocks and choose how you are buying mortar. The calculator uses NCMA’s rules of thumb for face-shell bedding, where mortar goes on the two face shells of each block, and allows for normal waste.
Mortar calculator
How it works
NCMA TEK 4-2A gives the approximate number of units one batch of mortar will lay (Table 2):
- Preblended mortar, 80 lb bag: about 16 standard CMU, or 50 brick-sized units
- Masonry cement (70 lb bag) with sand: about 30 standard CMU per bag; 8 bags of masonry cement to 1 ton of sand lays about 240 units
- Portland cement and lime: one 94 lb bag of portland cement with about half a 50 lb bag of hydrated lime and 4-1/4 cu ft of sand lays about 62 hollow units
Bags = number of units ÷ units per bag, rounded up.
Worked example
The 189 blocks from the cinder block calculator's example, laid with preblended mortar mix:
- Number of blocks: 189
- Block type: Standard 8 x 16 in face block
- Mortar you are buying: Preblended mortar mix, 80 lb bags
The calculator gives:
- 80 lb bags of mortar mix: 12
- Rate used: about 16 units per bag
189 ÷ 16 = 11.8, so 12 bags of 80 lb mortar mix. With masonry cement it would be 7 bags and just under a ton of sand.
Material and waste notes
- These are rules of thumb. Mason skill, joint tolerance, corners and returns all change how much you use (NCMA TEK 4-2A).
- Full mortar bedding, used for the first course on a footing and for some grouted walls, uses more than face-shell bedding.
- NCMA suggests adding half a ton of sand for waste if you use more than 3 tons; for smaller amounts, round up.
- Mortar type (M, S, N or O) is chosen for strength and exposure. Follow your plans or local code.
Frequently asked questions
How many blocks does an 80 lb bag of mortar lay?
About 16 standard 8 × 8 × 16 in blocks with face-shell bedding, according to NCMA TEK 4-2A.
How much sand for a bag of masonry cement?
NCMA gives 1 ton of masonry sand for every 8 bags of masonry cement, which works out to about 250 lb of sand per bag.
How much mortar per 100 blocks?
About 7 bags of 80 lb preblended mortar, or 4 bags of masonry cement with half a ton of sand.
Sources
Last reviewed: 25 September 2026. The calculation is covered by automated tests with known answers taken from the sources above. Found an error? Please let us know.