Mortar Calculator
Work out how many bags of mortar mix you need to lay your bricks or blocks. Enter the number of units and bag size for an instant bag count with waste allowance.
Updated 2026-06-14 · Free · No sign-up · Runs privately in your browser
Show the formula & steps
How the Mortar Calculator Works
This calculator estimates how many bags of mortar mix you need to lay a wall of bricks or concrete blocks. Enter how many units you are laying, choose your bag size, and add a waste allowance. It returns the number of bags and the total weight of mix.
The Formula
The estimate is built on a simple, well-known masonry rule of thumb:
Units to buy = unit count × (1 + waste% ÷ 100) Bags = ceil(units to buy ÷ yield per bag)
An 80 lb bag of standard mortar mix lays about 30 standard bricks or 12 standard 8×8×16-inch blocks with a 3/8-inch joint. Smaller bags lay proportionally fewer units.
Worked Example
For 500 standard bricks, an 80 lb bag, and a 10 percent waste allowance:
- Units to buy = 500 × 1.10 = 550 bricks
- Yield = 30 bricks per 80 lb bag
- Bags = ceil(550 ÷ 30) = ceil(18.3) = 19 bags
- Total weight = 19 × 80 = 1,520 lb of mix
Bricks vs. Blocks
Blocks are larger, so each one needs more mortar across its face and head joints. That is why a bag that lays 30 bricks lays only about 12 blocks. Always select the correct unit type so the yield matches your project.
What Affects the Result
- Joint thickness — wider joints consume more mortar and lower the yield.
- Bricklayer technique — heavy buttering uses more mortar than tight, full-bed joints.
- Re-pointing and repairs — extra mortar is needed for finishing and touch-ups.
| Project | Units | Approx. 80 lb bags |
|---|---|---|
| Small wall | 250 bricks | ≈ 10 bags |
| Garden wall | 500 bricks | ≈ 19 bags |
| Block wall | 500 blocks | ≈ 46 bags |
Frequently asked questions
How many bricks does a bag of mortar lay?+
An 80 lb bag of standard mortar mix lays about 30 to 37 standard bricks with a 3/8-inch joint. As a planning figure, use roughly 30 bricks per 80 lb bag, then add a waste allowance for spillage and mixing.
How much mortar do I need for concrete blocks?+
An 80 lb bag of mortar mix lays about 12 standard 8×8×16-inch blocks. For a wall of 500 blocks you would need roughly 500 ÷ 12 = 42 bags before adding any waste allowance.
Why add a waste allowance for mortar?+
Some mortar is always lost to spillage, mixing, dropped joints and re-pointing. A 10 percent waste allowance is typical, so 500 bricks plus 10 percent becomes 550 bricks worth of mortar to order.
Does joint thickness change how much mortar I need?+
Yes. Thicker joints use more mortar, so the bricks-per-bag yield falls. The standard 3/8-inch joint gives the figures used here; for wider joints reduce the yield and order more bags.
What is the difference between mortar and concrete?+
Mortar is a mix of cement, lime and sand used to bond bricks and blocks together. Concrete adds coarse aggregate (gravel) and is used for structural pours like footings and slabs, not for laying masonry joints.