Use this masonry mortar calculator: start from the wall size or from how many blocks or bricks you are laying to see how many bags of mortar mix to buy.
How to use the mortar calculator
- Choose whether you know the wall size or the number of units you are laying.
- Pick concrete block or modular brick — the calculator uses 1.125 blocks or 6.75 bricks per square foot of wall face.
- Check the units-per-bag figure against your mortar bag. It changes with joint thickness and how clean your work is.
- Add extra for dropped mortar, then enter a price per bag for a cost estimate.
Formulas
Units = wall face area (ft²) × units per ft² Bags = units ÷ units per bag × (1 + extra % ÷ 100), rounded up Sand (yd³) = bags × bag weight × 3 ÷ 2,700
Bagged mortar mix already contains sand, so the sand figure only applies if you are mixing masonry cement with sand on site at the usual one-to-three ratio. Ignore that row if you are buying ready-mixed bags.
Worked example: a 20 × 8 ft block wall
- Wall face: 20 ft × 8 ft = 160 ft².
- Blocks: 160 × 1.125 = 180 blocks.
- Bags at 28 blocks per bag: 180 ÷ 28 = 6.4, so 7 bags of 80 lb.
- Total weight: 7 × 80 = 560 lb.
How far a bag goes
An 80 lb bag of mortar mix lays roughly 25 to 30 standard 8 × 8 × 16 in blocks, or somewhere around 110 to 130 modular bricks, with a normal 3/8 in joint. Thicker joints, rough block and a lot of dropped mortar pull that number down fast, which is why the field is editable and why an extra allowance is worth keeping.
Quick reference
| Wall face area | Blocks | 80 lb bags at 28 per bag |
|---|---|---|
| 50 ft² | 57 | 3 |
| 100 ft² | 113 | 5 |
| 160 ft² | 180 | 7 |
| 250 ft² | 282 | 11 |
| 500 ft² | 563 | 23 |
Includes a 10% extra allowance. Brick walls need roughly six times as many units for the same area.
Questions
How many blocks does one bag of mortar lay?
Roughly 25 to 30 standard 8 × 8 × 16 in blocks per 80 lb bag with a 3/8 in joint. Use the lower figure if your joints run thick or the block is rough.
How many bricks does a bag of mortar lay?
About 110 to 130 modular bricks per 80 lb bag. Bricks have far more joint per square foot than block, so brickwork uses more mortar for the same wall area.
Do I need sand as well as mortar mix?
Not if you buy bagged mortar mix — the sand is already in it. You only buy sand separately when you are mixing masonry cement yourself, usually one part cement to three parts sand.
How much mortar do I need for 100 blocks?
About 4 bags of 80 lb mix at 28 blocks per bag, or 5 bags once you add 10% for waste.
Type S or Type N mortar?
Type S (about 1,800 psi under ASTM C270) suits foundations, retaining walls and below-grade block; Type N (about 750 psi) is the usual choice for above-grade brick veneer and general walls. Bag coverage is about the same for both.
How many bags of mortar per 1,000 bricks?
At 110–130 bricks per 80 lb bag, 1,000 modular bricks take roughly 8–9 bags. Enter your count above for an exact figure with waste.
Sources
- CMU-TEC-001-23: Concrete Masonry Unit Shapes, Sizes, Properties, and Specifications, Concrete Masonry & Hardscapes Association, Dec 12, 2024.
Used for: Nominal vs. specified block sizes and 3/8 in mortar joints. - Landscape Materials Density Chart, North Bay Materials.
Used for: Weight per cubic yard of sand, for the on-site mixing estimate. - NIST Guide to the SI, Appendix B.8: Factors for units listed alphabetically, National Institute of Standards and Technology.
Used for: Exact inch and foot definitions and the metric conversions.