Mortar Calculator
Say what you are laying and how many units, and this gives the bags of mortar mix, the sand to go with it, and the mortar type to ask for.
Take this list to the store
We'll email the quantities above, what you typed in, and a link that reopens this calculator already filled in — so you can adjust it on your phone in the aisle.
How to work it out
-
Count the units
Blocks or bricks for a wall, square feet for stone veneer or repointing. The block and brick calculators work the counts out if you only have wall dimensions.
-
Pick the mortar type
Type N for ordinary above-grade walls, Type S where there is soil or wind load, Type M for foundations and heavy stone, Type O only for interior work and old soft brick.
-
Mix small batches
Mortar starts stiffening in about 90 minutes and cannot be retempered indefinitely. Mix what you can lay in an hour, and keep the board covered in the sun.
-
Keep the joints consistent
These figures assume 3/8 in joints. Half-inch joints use roughly a third more mortar, and irregular stone can double it.
Coverage per 80 lb bag
Working figures for 3/8 in joints.
| Laying | Per 80 lb bag | Bags per 100 units |
|---|---|---|
| 8×8×16 block | about 8 blocks | 13 bags |
| Standard brick | about 27 bricks | 4 bags |
| Modular / queen brick | about 16 bricks | 7 bags |
| Stone veneer | about 2.2 sq ft | 46 bags per 100 sq ft |
| Repointing | about 9 sq ft | 12 bags per 100 sq ft |
Mortar types
Strength is not the goal — mortar should be weaker than what it joins, so cracks run in the joint and not through the brick.
| Type | Strength | Use it for |
|---|---|---|
| Type M | 2,500 psi | Foundations, retaining walls, heavy stone, below grade |
| Type S | 1,800 psi | Below grade, patios, walls that take wind or soil load |
| Type N | 750 psi | General above-grade walls, chimneys, soft brick |
| Type O | 350 psi | Interior non-load-bearing, repointing historic masonry |
How much mortar per block or brick?
An 80 lb bag of mortar mix lays about 8 standard blocks, or about 27 standard bricks, with 3/8 in joints. A 100 block wall therefore takes 13 bags.
Those are working numbers used on site, not laboratory figures. Rough block, wide joints, hot weather and a first-time hand all push the usage up, which is why 10% extra is the default here.
Mortar mix or masonry cement?
Mortar mix in a bag already contains the sand — add water only. It is the simple option for anything under a few hundred units.
Masonry cement is cement without sand, mixed roughly 1 part cement to 3 parts mason sand by volume. It is cheaper on a big job, which is why the sand figure is shown above.
Do not use the strongest mortar
The common mistake is reaching for Type M or S because they are stronger. Mortar is meant to be the sacrificial part of a wall: softer than the units, so that movement cracks the joint, which can be repointed, rather than the brick, which cannot.
On old soft brick, a hard modern mortar will spall the faces off within a few winters. Use Type O or a lime mortar for repointing anything historic.
How this is worked out
No black box — here is the arithmetic the calculator runs, so you can check it against your own numbers.
-
bags = units ÷ units per bagCoverage figures for 3/8 in joints. -
× (1 + extra %)Spillage, joints wider than planned, and the board at the end of the day. -
mortar volume = bags × 0.6 cu ftAn 80 lb bag makes roughly 0.6 cubic feet of mortar. -
sand = volume × 0.9Only when mixing from masonry cement rather than pre-mixed bags.
Common questions
How many blocks does a bag of mortar lay?
About 8 standard 8×8×16 blocks per 80 lb bag with 3/8 in joints, so roughly 13 bags per 100 blocks.
How many bricks per bag of mortar?
About 27 standard bricks per 80 lb bag, or around 16 for larger modular and queen sizes.
What is the difference between Type N and Type S mortar?
Strength and where they belong. Type N is about 750 psi and suits ordinary above-grade walls; Type S is about 1,800 psi and is used below grade or where soil and wind loads apply.
How much sand do I need for mortar?
Mixing from masonry cement, about 3 parts sand to 1 part cement by volume — roughly 0.9 cubic feet of sand per 80 lb bag equivalent. Bagged mortar mix already includes it.
How much water goes in a bag of mortar?
Around a gallon per 80 lb bag, added gradually until it holds a ridge without slumping. Too much water is the commonest cause of weak joints.
How long can I use mixed mortar?
About 90 minutes at room temperature, less in heat. You can add a little water once to bring it back; after that it is done.
What mortar should I use for repointing?
Match what is there. Modern brick can take Type N; old soft brick needs Type O or a lime mortar. A harder mortar than the brick will damage the wall.
How much mortar for stone veneer?
About 2.2 sq ft per 80 lb bag including the scratch coat, so roughly 46 bags per 100 sq ft. Deep irregular stone uses more.
Where these figures come from
Every figure below is traceable. How we check the numbers explains how they are verified, and the coverage reference collects them all in one place.
- ASTM C270 Standard Specification for Mortar for Unit Masonry — mortar types N, S, M and O and their compressive strengths
- Portland Cement Association and bagged-product data sheets — coverage per bag and mixing proportions
- National Park Service Preservation Brief 2 — why repointing mortar must be softer than the masonry
Think a number here is wrong? Tell us — we check every report, correct the page, and date the change. Last checked September 27, 2026.