Mortar Calculator
Calculate how many 80-lb bags of mortar mix you need for a block or brick wall based on its area, plus total cost.
How this calculator works
An 80-lb bag of standard mortar mix lays approximately 25 sq ft of block wall at typical 3/8 in joint widths — around 28 standard blocks per bag. This calculator divides your wall’s area by that coverage rate to get the bag count.
Formula: Bags = Wall area (sq ft) ÷ 25 sq ft per bag.
Worked example
A wall 20 ft long x 8 ft high (160 sq ft):
- Area: 20 × 8 = 160 sq ft
- Bags: 160 ÷ 25 = 6.40 bags
- At $9/bag, that’s $57.60.
Coverage reference
| Wall area | Bags needed (~25 sq ft/bag) |
|---|---|
| 10 x 4 ft | 1.60 bags |
| 20 x 8 ft | 6.40 bags |
| 40 x 16 ft | 25.60 bags |
How to measure your wall
Measure the wall’s total length and height in feet — length in the Length field, height in the Width field — to get the total square footage the calculator divides by bag coverage. If you’re working with brick rather than block, budget extra beyond this number, since brick’s thinner units mean more mortar joint per square foot of finished wall than the block-wall rate this calculator uses.
Frequently asked questions
How much wall does one bag of mortar cover?
An 80-lb bag of mortar mix covers roughly 25 sq ft of standard 8 in CMU block wall, which works out to about 28 blocks per bag at typical 3/8 in mortar joints. Brick walls use noticeably more mortar per square foot since brick joints are more numerous relative to unit size.
Type N or Type S mortar — which do I need?
Type N is the general-purpose mortar for most above-grade, non-load-bearing walls like garden walls and veneer — it's easier to work with and what most DIY block or brick projects use. Type S is higher-strength and required for load-bearing walls, foundations, retaining walls, or anywhere exposed to higher wind or seismic loads; check local code before choosing.
Does this calculator work for brick walls too?
The 25 sq ft per bag figure is calibrated for standard block wall joints. Brick has thinner units and more joint length per square foot, so brick walls typically use more mortar per bag-equivalent — treat this calculator's output as a block-wall estimate and add extra margin if you're mortaring brick.
Why doesn't this calculator round bags up to a whole number?
Mortar bags are shown to two decimal places rather than rounded up, since it's common (and often cheaper) to buy mortar by the pallet or in bulk quantities rather than bag-by-bag, and many masons blend leftover mortar across small jobs. Round up yourself if you're buying individual 80-lb bags at a retail store.
Should I add extra mortar for a first-time DIY pour?
Yes, even though this calculator doesn't apply a waste toggle for mortar — first-time mixing and spreading tends to waste more material than a professional's practiced technique, through over-mixing, spillage, and joints that need re-pointing. Buying one extra bag beyond the calculated amount is a reasonable safety margin.
Estimates only. Verify quantities with your supplier before purchasing.