Mortar Calculator
Use this mortar calculator to work out how much a brick or block job needs, as premixed bags or as portland, lime and sand mixed on site.
Mortar for Brick
Mortar for Block
Concrete block takes far less mortar per square foot than brick, because there are far fewer joints.
From Wall Area
When you know the wall but have not counted the units yet.
How to use the Mortar Calculator
Enter how many bricks or blocks you are laying, or the wall area if you have not counted units yet. The calculator gives the answer two ways at once, because there are two different products called mortar.
Premixed mortar comes in a bag with the sand already in it. You add water. It is convenient, expensive per unit laid, and right for small jobs.
Site-mixed mortar is portland cement and lime bought separately and mixed with your own sand. Far cheaper at volume, and what any serious quantity of masonry is laid with.
Mortar formula
Premixed:
bags = units ÷ units per bag × (1 + waste%)
Site-mixed, from the classic 1,000 brick figures:
portland bags = units ÷ 1,000 × 7(brick)sand = units ÷ 1,000 × 1 cubic yard(brick)
| Unit | Per 80 lb premix bag | Per 1,000 units, site-mixed |
|---|---|---|
| Modular brick | 30 bricks | 7 bags portland + 1 yd³ sand |
| Concrete block | 12 blocks | 17.5 bags portland + 2.5 yd³ sand |
The block site-mix figures are derived from the brick ones: a block takes 30 ÷ 12 = 2.5 times the mortar of a brick, so it takes 2.5 times the cement and sand.
Units per square foot, if you are working from wall area: 6.75 modular bricks or 1.125 standard 8 × 8 × 16 blocks.
Worked example
1,000 modular bricks with a 10% allowance:
- Premixed: 1,000 ÷ 30 = 33.3, plus 10% = 36.7, so 37 bags of 80 lb
- Site-mixed: 8 bags of portland cement and about 1.1 yd³ of sand
A 20 ft × 8 ft brick wall is 160 sq ft, or 1,080 bricks, 40 bags of premix.
200 concrete blocks: 200 ÷ 12 = 16.7, plus 10% = 19 bags.
What the result means
The two answers are not in conflict, they are two different products. A bag of premixed mortar already contains the sand. A bag of portland cement does not, which is why the bag count is a fifth as high and there is a pile of sand to go with it.
Premix is right for a garden wall, a repair, or anything under a few hundred units. Site mixing wins on price at volume and is what any real masonry job uses, but it needs a mixer, somewhere to put a yard of sand, and someone who can gauge a batch consistently.
Block takes 2.5 times the mortar per unit that brick does, but far less per square foot of wall, a block covers about six times the area of a brick with only two and a half times the mortar. That is most of why block is cheaper to lay.
Every figure here is a working estimate. Joint thickness, unit absorbency, how much gets dropped and how much goes off on the board all move it. Ten percent waste is not padding, it is what happens.
Common mistakes
- Buying portland cement when the calculator said premix, or the reverse. They are different products with different bag counts. Check which figure you are reading.
- Forgetting the sand. Site-mixed mortar needs roughly a cubic yard of masonry sand per 1,000 bricks. It is easy to buy the cement and not the sand.
- Mixing more than you can lay. Mortar starts going off within a couple of hours. Retempering with water once is acceptable; twice is not.
- Using the wrong mortar type. Type N for most above-grade work, Type S where there is more structural load or contact with soil. Stronger is not automatically better, mortar should be weaker than the units it joins.
- Ignoring waste. Ten percent is realistic on a job of any size, and more on repointing or awkward work.
Frequently asked questions
How much mortar do I need per 1,000 bricks?
About 33 bags of 80 lb premixed mortar, or 37 with a 10 percent allowance. Mixing on site instead, it is roughly 7 bags of portland cement plus a cubic yard of masonry sand. Both figures are right, they are different products.
How many blocks does a bag of mortar lay?
About 12 concrete blocks per 80 lb bag of premixed mortar, against about 30 bricks from the same bag. A block takes 2.5 times the mortar of a brick because the units are bigger, though far less mortar per square foot of wall.
How many bricks does one bag of mortar lay?
Roughly 30 modular bricks per 80 lb bag of premix at a standard 3/8 inch joint. A 60 lb bag lays about 22. Thicker joints and absorbent bricks reduce it.
What is the difference between mortar mix and portland cement?
Mortar mix is a premixed product containing cement, lime and sand, you add only water. Portland cement is one ingredient; you add lime and sand yourself. That is why one job needs 33 bags of the first or 7 of the second.
What type of mortar should I use?
Type N for most above-grade residential work. Type S where there is greater structural load or contact with soil. Mortar is meant to be weaker than the masonry it joins, so reaching for the strongest available is usually the wrong instinct.
Sources and assumptions
Premixed coverage of about 30 bricks or 12 blocks per 80 lb bag follows typical manufacturer figures for standard joints, and matches the block figure used across this site.
The site-mixed figure of roughly 7 bags of portland plus a cubic yard of sand per 1,000 bricks is a long-standing masonry estimating convention. The block equivalent is derived from it by the 2.5:1 mortar ratio between the two units, rather than taken from a separate source.
All of these move with joint thickness, unit absorption and workmanship. Treat them as estimates and confirm before ordering.