Mortar Calculator
Calculate how many bags of mortar mix you need for your wall project.
Enter wall area and joint thickness to get accurate estimates.
Mortar is the binding material used between bricks, blocks, and stones in masonry construction. The mortar mix ratio, meaning the proportion of cement, sand, and sometimes lime, determines strength, workability, and durability for specific applications.
Standard mortar mix types (ASTM (American Society for Testing and Materials) C270):
| Type | Cement : Lime : Sand | Compressive Strength | Best Use |
|---|---|---|---|
| Type S | 1 : 0.5 : 4.5 | ~1,800 PSI (Pounds per Square Inch), 12.4 MPa (Megapascals) | Below grade, load-bearing, retaining walls |
| Type N | 1 : 1 : 6 | ~750 PSI (5.2 MPa) | Above-grade exterior walls, chimneys |
| Type M | 1 : 0.25 : 3 | ~2,500 PSI (17.2 MPa) | Foundations, sewers, harsh weather |
| Type O | 1 : 2 : 9 | ~350 PSI (2.4 MPa) | Interior, non-load-bearing, repointing soft brick |
Mortar volume calculation:
Mortar Volume = Wall Area × Joint Area Fraction
For standard face brick (8" × 2.25") with 3/8" joints, the mortar occupies approximately 17% of wall face area (joints between bricks plus beds).
Simplified coverage formula:
80 lb (36 kg) bag covers ≈ 12–14 sq ft (1.1–1.3 m²) of standard brick wall at 3/8" joints.
90 lb (41 kg) bag of pre-mix covers ≈ 14–16 sq ft
Coverage by joint thickness, face brick:
| Joint Thickness | Coverage per 80 lb bag |
|---|---|
| 1/4" (6 mm) | ~18–20 sq ft (1.7–1.9 m²) |
| 3/8" (10 mm) | ~12–14 sq ft (1.1–1.3 m²) |
| 1/2" (13 mm) | ~9–11 sq ft (0.84–1.0 m²) |
| 5/8" (16 mm) | ~7–9 sq ft (0.65–0.84 m²) |
Concrete block is a completely different number, and this is the mistake to avoid. A single 8×8×16 CMU covers the same wall face as six bricks but needs two joints instead of twelve, so a block wall drinks about a fifth of the mortar per square foot. The masonry rule of thumb is 3 bags of 80 lb mix per 100 blocks at a 3/8 inch joint. A hundred blocks face 88.9 sq ft, which works out to roughly 29.6 sq ft per bag against 14 for brick.
Run a block wall through the brick column and you will buy something like three times the mortar you need. That is why the calculator above asks which unit you are laying before it asks for the area. The concrete block wall calculator works from block count instead of wall area and lands on the same figure.
Water ratio for mixing:
- Type N pre-mix: approximately 5–6 quarts (4.7–5.7 L) of clean water per 80 lb bag
- Mix to a peanut butter consistency: mortar should hold its shape when squeezed but not be crumbly or soupy
- Avoid over-watering: excess water weakens mortar and causes cracking
Worked example: A garden wall: 20 ft × 4 ft = 80 sq ft of face area, using standard brick, 3/8" joints. Bags needed = 80 sq ft ÷ 14 sq ft per bag = 5.7 → 6 bags Add 10% waste: 6 × 1.10 = 6.6 → 7 bags to buy
The same 80 sq ft in 8×8×16 block: 80 ÷ 29.6 = 2.7 → 3 bags, plus waste → 4 bags. Ninety blocks instead of 540 bricks, and roughly half the mortar. On a big wall that ratio is where the money is.
Repointing (tuckpointing): Old mortar must be removed to a depth of at least 3/4" (19 mm) before new mortar is applied. Use Type N or Type O for repointing. The new mortar should be softer than the surrounding brick, so that moisture and thermal movement go into the joint rather than the brick face. Never use high-strength Type S or Type M on old or soft brick. It will spall the brick, which is surface flaking, and a spalled brick has to come out of the wall.
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