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 — the proportion of cement, sand, and sometimes lime — determines strength, workability, and durability for specific applications.
Standard mortar mix types (ASTM C270):
| Type | Cement : Lime : Sand | Compressive Strength | Best Use |
|---|---|---|---|
| Type S | 1 : 0.5 : 4.5 | ~1,800 PSI (12.4 MPa) | 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:
| 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) |
Water ratio for mixing:
- Type N pre-mix: approximately 6–7 quarts (5.7–6.6 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 / 13 sq ft per bag = 6.2 bags → buy 7 bags Add 10% waste: 7 × 1.10 = 8 bags minimum (buy 8–9)
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 mortar for repointing — it should be softer than the surrounding brick to allow moisture and thermal movement without cracking the brick face. Never use high-strength Type S or Type M for repointing old or soft brick — it will cause spalling (surface flaking) of the brick.