Mortar Calculator

Enter your brick count and joint dimensions to calculate the mortar volume and number of bags needed. Uses the industry-standard estimate of one 70 lb bag per 35 standard bricks.

What is Mortar?

A mortar calculator estimates how much mortar mix is required for a brick or block masonry project. Mortar is the binding paste made from Portland cement, hydrated lime, sand, and water that fills the joints between masonry units. Getting the mortar quantity right is critical because excess mortar has a limited working life once mixed — typically 90 minutes before it begins to set — and running short mid-project forces an unplanned trip to the supplier while partially completed joints dry out and weaken. The industry-standard estimating method is based on empirical coverage rates rather than geometric joint volume calculations. For standard modular bricks (8 x 2-1/4 x 3-5/8 inches) with 3/8-inch joints, one 70-pound bag of mortar mix covers approximately 35 bricks, and one 80-pound bag covers approximately 40 bricks. These rates account for both the bed joints (horizontal layers) and head joints (vertical joints between bricks in the same course), as well as typical waste from tooling and cleaning. Each 70-pound bag of pre-mixed mortar yields approximately 0.50 cubic feet of wet mortar, while an 80-pound bag yields approximately 0.60 cubic feet. Pre-mixed bags (such as Quikrete Type S or Type N) contain Portland cement, hydrated lime, and sand in the correct proportions — you only add water. For large projects, masons often buy the components separately and mix on site, but pre-mixed bags are standard for residential and small commercial work. Mortar type matters as much as quantity. Type N mortar (medium strength, 750 PSI) is the general-purpose choice for above-grade exterior walls and interior load-bearing walls. Type S mortar (high strength, 1,800 PSI) is required for below-grade applications, retaining walls, and areas subject to high wind or seismic loads. Type M mortar (very high strength, 2,500 PSI) is used for foundations and heavy structural applications but is less workable and rarely needed in residential construction. Joint width affects mortar consumption significantly. A 1/2-inch joint uses roughly 30-40% more mortar than a 3/8-inch joint for the same number of bricks. This calculator uses the standard industry rate per brick, which assumes 3/8-inch joints. For wider joints, increase the estimate proportionally or add a generous waste factor. Temperature and humidity also affect mortar usage. Hot, dry conditions cause faster evaporation and may require slightly wetter mixes, while cold weather (below 40 degrees F) requires special cold-weather additives and protection during curing.

How to Calculate

1. Count or estimate the total number of bricks for your project
2. Confirm the mortar joint width (3/8 inch is the most common standard)
3. Confirm the mortar joint depth (typically matches the joint width)
4. Review the mortar volume in cubic feet
5. Choose between 70 lb bags (covers 35 bricks each) or 80 lb bags (covers 40 bricks each)
6. Add 10-15% extra for waste if you are less experienced with mortar application

Formula

Mortar Volume (cu ft) = (Brick Count / 35) x 0.5 70 lb Bags = ceiling(Brick Count / 35) 80 lb Bags = ceiling(Brick Count / 40) Where 35 bricks per 70 lb bag and 40 bricks per 80 lb bag are the industry-standard coverage rates for standard modular bricks with 3/8-inch mortar joints. Each 70 lb bag yields 0.5 cu ft and each 80 lb bag yields 0.6 cu ft of mixed mortar.

Example Calculation

A project using 1,000 standard modular bricks with 3/8-inch joints: Mortar Volume = (1,000 / 35) x 0.5 = 28.57 x 0.5 = 14.29 cu ft 70 lb Bags = ceil(1,000 / 35) = ceil(28.57) = 29 bags 80 lb Bags = ceil(1,000 / 40) = ceil(25) = 25 bags

Frequently Asked Questions