Mortar Calculator
Calculate the mortar needed to lay brick or block, in bags and volume. Enter the wall area or unit count and the calculator estimates mortar based on typical joint sizes. Pairs with the concrete block and brick calculators for a full masonry order.
Mortar Diagram
How the Formula Works
Calculate wall area
Wall Area = Length × Height Measure the face area of the wall in square feet. For openings like windows and doors, you may deduct them if they are significant — for small openings, leaving them in provides a useful safety buffer.
Apply joint factor
Mortar Volume (net) = Wall Area × Joint Factor The joint factor represents cubic feet of mortar per square foot of wall face. It varies by unit type and joint width: standard 3/8″ brick ≈ 0.025 ft³/ft², CMU block ≈ 0.012 ft³/ft², stone with 3/4″ joints ≈ 0.060 ft³/ft². Use the Custom option for unusual specs.
Apply waste factor
Adjusted Mortar = Net Mortar × (1 + Waste %) Use 15% for standard masonry work. Increase to 20% or more for stone, irregular units, complex patterns, or when mixing by hand where spillage is more likely.
Calculate bags required
Bags = ⌈Adjusted Mortar ÷ Yield per Bag⌉ An 80 lb bag of mortar mix yields approximately 0.60 ft³; a 60 lb bag yields 0.45 ft³. Always round up — you cannot use a partial bag, and running short mid-course causes weak joints.
Estimate unit count
Units = ⌈Wall Area × Units per ft²⌉ Standard modular brick ≈ 6.75 bricks/ft² with 3/8″ joints. CMU 8×8×16 block ≈ 1.125 blocks/ft². The unit count includes the waste factor so you order enough material in one trip.
Frequently Asked Questions
For standard brick with 3/8″ joints, plan on approximately 0.025 ft³ of mortar per square foot of wall face. A 100 ft² wall needs about 2.5 ft³ of net mortar — roughly 5 bags of 80 lb mix before waste.
An 80 lb bag yields 0.60 ft³. For a 100 ft² standard brick wall: 2.5 ft³ net ÷ 0.60 = 5 bags net. With 15% waste that rounds up to 6 bags. Use this calculator to get an exact count for your wall dimensions.
Type S is recommended for below-grade and exterior applications where strength and moisture resistance matter. Type N is the standard general-purpose exterior mortar. Type M is used for load-bearing and below-grade heavy-duty work. Type O is for interior non-load-bearing applications only.
3/8″ is the standard joint thickness for both brick and CMU block. A 1/2″ joint is also acceptable for both. Stone joints vary widely — 1/2″ to 3/4″ is typical for ashlar; rubble stone may use joints up to 1″ thick.
Pre-mixed bags: add water per the label — typically 4–5 quarts per 80 lb bag. Site-mixed Type N mortar: 1 part Portland cement + 1 part hydrated lime + 6 parts masonry sand. Mix dry first, then add water gradually until the mix holds its shape but slides cleanly off a trowel.
Standard modular brick (3-5/8″ × 2-1/4″ × 7-5/8″) lays at approximately 6.75 bricks per square foot with 3/8″ mortar joints. With 1/2″ joints the count drops slightly to about 6.55 bricks/ft².
A standard 80 lb bag of mortar mix typically costs $8–$12 at home improvement stores. A 100 ft² brick wall needs roughly 6 bags with waste, putting mortar material cost at $50–$75. Labour and additional materials (brick, block) are separate.
Mortar is used to bond masonry units together — it fills the joints between bricks, blocks, or stones and provides structural adhesion. Grout fills cavities inside CMU cores or the gaps in tile installations. The two mixes have different proportions and are not interchangeable.
References
- ASTM International ASTM C270 – Standard Specification for Mortar for Unit Masonry
- The Masonry Society TMS 402 – Building Code Requirements for Masonry Structures