Mortar Calculator
Estimate how much mortar a brick or block wall needs, either from the wall area or from a direct count of bricks or blocks, in metric (m²) or imperial (sq ft) units. Get the bags to buy, the placed volume and weight, the raw cement, lime and sand for the ASTM mortar type you pick, and an optional material cost.
Formula
Worked example
100 sq ft of modular brick: 100 × 7 = 700 bricks. 700 ÷ 36 per 80 lb bag = 19.4 bags. With 10% waste, 19.4 × 1.10 = 21.4, round up to 22 bags, about 13.2 cu ft of placed mortar.
How the mortar estimate works
The calculator works in three moves. First it sets a count of bricks or blocks: either from the wall face area using a coverage figure for the masonry you pick (a standard modular brick laid with 3/8 inch joints takes about 7 bricks per square foot, an 8 by 16 inch concrete block about 1.125 blocks), or straight from a number you already have. Then it divides that count by how many units a single bag of pre-mixed mortar typically lays, around 36 modular bricks or 12 blocks for an 80 pound bag. Finally it multiplies by a waste allowance and rounds up to whole bags, because mortar is sold whole and any left mixed in the tub sets up before the next course. It also reports the placed volume and total weight so you can plan storage and delivery.
Mortar types and mixing from raw materials
If you mix on site rather than buy pre-mix, the type of mortar sets the cement, lime and sand proportions. ASTM recognises four common types: Type O is a soft, low strength mix (about 350 psi) for interior and non-load-bearing work, Type N is the general purpose choice for most above-grade walls (about 750 psi), Type S is stronger for below-grade and structural work (about 1,800 psi), and Type M is the strongest (about 2,500 psi) for heavy loads and foundations. The calculator splits the dry ingredient volume by the cement to lime to sand ratio of the type you choose, for example 1:1:6 for Type N, so you can order portland cement and hydrated lime in pounds and masonry sand in cubic yards. Dry ingredients run roughly a third more than the placed wet volume, which the tool accounts for.
What changes the number of bags, and costing the job
These yields are averages, not guarantees. Thicker joints, rough or hand-made bricks, cold or windy weather that stiffens the mix, and learner bricklayers who over-butter all push the count up, so a generous waste allowance is wise on a first project. A double-wythe wall, two bricks thick, uses roughly twice the mortar of the single-wythe estimate here, and a 60 pound bag holds about three quarters of an 80 pound bag, which the tool accounts for. Turn on the cost estimate and enter your price per bag to get a planning figure for the pre-mixed mortar; sand, lime, delivery and tax are extra and local prices vary, so confirm quantities and prices with your supplier before you order.
Masonry coverage and mortar yield (3/8 in joints)
| Brick or block | Units per sq ft | Units per 80 lb bag |
|---|---|---|
| Modular brick | 7 | 36 |
| Queen brick | 5.76 | 33 |
| King brick | 4.8 | 30 |
| Utility brick | 3 | 22 |
| 4 in concrete block | 1.125 | 16 |
| 6 in concrete block | 1.125 | 13 |
| 8 in concrete block | 1.125 | 12 |
| 12 in concrete block | 1.125 | 11 |
Field averages for a single-wythe wall and an 80 lb bag of pre-mixed mortar.
Frequently asked questions
How many bags of mortar do I need for 100 square feet of brick?
For a single-wythe wall of standard modular brick with 3/8 inch joints, plan on roughly 19 to 22 bags of 80 pound pre-mixed mortar per 100 square feet once a 10% waste allowance is included. That comes from about 700 bricks at 7 per square foot, divided by the 36 bricks an 80 pound bag lays.
How many bricks does one bag of mortar lay?
An 80 pound bag of pre-mixed mortar lays roughly 36 modular bricks or about 12 standard concrete blocks with 3/8 inch joints. A 60 pound bag holds about three quarters as much. These are field averages, so neat work with tight joints stretches a bag further and sloppy work uses more.
What is the difference between Type N, S, O and M mortar?
They differ in their cement to lime to sand ratio and so in strength. Type O is soft and low strength (about 350 psi) for interior non-structural work, Type N is the general purpose mix (about 750 psi) for most above-grade walls, Type S is stronger (about 1,800 psi) for below-grade and structural use, and Type M is the strongest (about 2,500 psi) for foundations and heavy loads. Pick N unless your plans call for more.
How much cement, lime and sand do I need to mix my own mortar?
It depends on the mortar type. For Type N at a 1:1:6 cement:lime:sand ratio, the calculator splits the dry ingredient volume (about a third more than the placed mortar) by those parts and reports portland cement and hydrated lime in pounds and masonry sand in cubic yards, so you can order each material separately.
Should I add extra for waste?
Yes. A 10% allowance is standard to cover mortar that is spilled, dropped off the board, or that hardens in the tub before it can be used. On a first project, in cold or windy weather, or with rough hand-made brick, bump the allowance higher to avoid a second trip to the yard.