Mortar Bags Calculator
Enter your wall length and height to find how many bags of mortar you need for brick or block — plus a printable materials estimate.
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Mortar Bags Calculator
Short answer
For a 20 ft × 8 ft brick wall (160 ft²) at a standard 3/8 in joint, you’d need about 1,080 bricks, or roughly 1,188 with a 10% waste allowance — which comes to about 10 bags of 80 lb mortar. Switch to concrete block or enter your own coverage rate for a different unit.
Typical mortar bag yields
| Masonry unit | Units per ft² (single wythe) | Units per 80 lb bag |
|---|---|---|
| Standard modular brick (3/8 in joint) | ≈6.75 | ≈125 |
| 8x8x16 concrete block (3/8 in joint) | ≈1.125 | ≈33 |
These are widely used rule-of-thumb figures. Actual yield varies with joint thickness, mortar consistency, and how much is struck off versus left proud.
How the formula works
- Find the wall face area: length × height, minus any door/window openings.
- Multiply by the units-per-ft² figure for your masonry type to get the raw unit count.
- Add a waste allowance (commonly 10%) for spillage and tooling loss.
- Divide by the units-per-bag yield for your bag size, and round up to the next whole bag.
Worked example
A 20 ft × 8 ft brick wall, no openings, 10% waste, 80 lb bags:
Wall area = 20 × 8 = 160 ft². Units = 160 × 6.75 = 1,080 bricks. With 10% waste = 1,188 bricks. Bags = ceil(1,188 ÷ 125) = 10 bags.
Assumptions this calculator makes
- A standard 3/8 in mortar joint and a single-wythe (single layer) wall.
- Bag yield figures are rule-of-thumb averages, not a specific mortar brand’s spec sheet.
- No allowance for a scratch coat, parging, or repointing — this is for laying new units only.
- Door and window openings are subtracted as a flat area, not by exact frame geometry.
Common mistakes
- Forgetting to subtract door and window openings, which over-orders mortar and units.
- Using brick yield figures for block (or vice versa) — the two have very different mortar-joint surface area per unit.
- Skipping the waste allowance, then running short mid-job when the last bag doesn’t stretch far enough.
- Assuming a thicker joint uses the same yield as a 3/8 in joint — thicker joints need noticeably more bags.
FAQ
How many bricks does one bag of mortar lay?
An 80 lb bag of mortar typically lays about 125 standard modular bricks (3 5/8 x 2 1/4 x 8 in) with 3/8 in joints. This varies with joint thickness, brick size, and how much mortar is squeezed out versus struck off.
How many concrete blocks does one bag of mortar lay?
An 80 lb bag of mortar typically lays about 33 standard 8x8x16 in concrete masonry units (CMU) with 3/8 in joints, since blocks have far less mortar-joint surface area per unit than bricks do.
Why should I add extra for waste?
Some mortar is always lost to the mixing pan, trowel, joint tooling, and spillage. A 10 percent waste allowance is a common rule of thumb to avoid running short mid-job.
Does mortar joint thickness change how many bags I need?
Yes. Thicker joints use more mortar per unit, which lowers the number of units one bag can lay. The bag-yield figures used here assume a standard 3/8 inch joint; thicker joints will need more bags than this estimate.
Should I use 60 lb or 80 lb mortar bags?
Either works — this calculator lets you pick the bag size, and it scales the number of bags accordingly. 80 lb bags are more common for larger jobs since they yield more mortar per bag purchased.