Mortar Mix Calculator
Estimate the bags of mortar and tons of sand needed to lay a block or brick wall, based on how many units you are setting.
Reviewed by the ToolNestr Editorial Team — July 2026
How the mortar mix calculator works
Mortar is the bonding material spread in the joints between blocks or bricks. The amount you need depends mostly on how many units you are laying, because each unit gets a fairly consistent bed and head joint. Masonry suppliers publish coverage figures for this, and the calculator uses the widely accepted rule that one 80 lb bag of mortar lays about 33 standard blocks or 125 standard bricks at a 3/8-inch joint.
From your unit count it divides by that coverage to get bags, rounding up. A 60 lb bag holds three-quarters as much material, so it lays about three-quarters as many units. If you prefer to mix your own mortar from bagged masonry cement and loose sand, the calculator also estimates the sand: roughly one ton for every eight bags of cement.
Mortar strength is graded by ASTM C270 into types N, S, and M. Type N suits ordinary above-grade walls, Type S is used for below-grade and structural walls, and Type M is the strongest, for foundations and retaining walls. The quantity is the same regardless of type — pick the type from your wall's job, then use this tool for the count.
Pick block or brick
Choose which unit you are laying; each has its own coverage per bag.
Enter the count
Use the unit count from your wall calculator, plus a few percent for breakage.
Read bags and sand
Get bag count, and the sand estimate if you plan to mix your own mortar.
The formula explained
Bags for block
Bags = blocks ÷ 33 for 80 lb bags. Laying 200 blocks: 200 ÷ 33 = 7 bags (rounded up from 6.1).
Bags for brick
Bags = bricks ÷ 125 for 80 lb bags. Laying 500 bricks: 500 ÷ 125 = 4 bags.
Sand if mixing your own
Sand tons = bags ÷ 8. For 7 bags: 7 ÷ 8 = 0.88 tons of masonry sand.
Worked example
A block retaining wall using 450 standard 8-inch blocks, 80 lb bags.
Choosing the right mortar
Type N — general purpose
Medium strength for most above-grade walls, chimneys, and soft-brick veneer. The forgiving, all-round choice for typical exterior and interior walls.
Type S — structural
Higher strength and better bond for below-grade walls, foundations, and walls facing wind or soil pressure. A common upgrade for load-bearing masonry.
Type M — high strength
The strongest common type, for heavy loads, retaining walls, and hard stone. Strong in compression but less workable, so it takes more skill to tool.
Consistency matters
Whatever the type, mix to a plastic, workable consistency and use it within about 90 minutes. Over-wet or re-tempered mortar loses strength and bond.
Tips for ordering mortar
Coverage is an estimate, not a guarantee
Rough, absorbent block and thick joints burn through mortar faster than smooth units at a tight 3/8-inch joint. Treat the bag count as a starting point and buy a little extra.
Pre-mixed versus site-mixed
Bagged mortar mix already contains sand and is convenient for small jobs. On large walls, buying masonry cement plus bulk sand and mixing on site is cheaper — that is where the sand estimate matters.
Keep sand and cement dry
Damp or contaminated sand throws off the mix ratio, and wet cement bags harden into waste. Store both under cover and off the ground until you are ready to mix.
Real-world context
A full basement foundation wall shows the calculator's higher end: 600 standard 8-inch blocks need 600 ÷ 33 = 19 bags of 80 lb mortar mix — for a job this size, most masons buy masonry cement and bulk sand instead, since 19 bags of cement works out to about 2.4 tons of sand at the 1-ton-per-8-bags ratio.
A brick veneer accent wall shows a smaller, more typical DIY job: 1,000 standard bricks need 1,000 ÷ 125 = 8 bags — right in the range where bagged, pre-blended mortar mix is genuinely the more convenient choice over mixing cement and sand separately for a job this size.
Switching bag size changes the count more than people expect: the same 80-block garden wall job needs only 3 bags of 80 lb mortar mix (80 ÷ 33, rounded up), but 4 bags of 60 lb mix, because the lighter bag only covers about 75% as many units — buying by the cheaper-looking bag price without checking coverage per bag can mean paying for more bags overall.
Common misconceptions
"Mortar Type M is the best choice since it's the strongest." Stronger isn't automatically better. Type M is harder and less workable than Type N, and using it where a wall doesn't need that strength makes the mortar harder to tool and more brittle than necessary — match the type to the wall's actual structural demand, not to "more strength is safer."
"Once mortar starts to stiffen in the pan, adding a splash of water fixes it." Only within its working window. Mortar can be re-tempered with a little water within roughly the first 90 minutes after mixing, but once it starts to set chemically, adding water doesn't restore workability — it just weakens the bond, so mortar that's gone past its working time should be discarded, not revived.
Related calculators
Frequently asked questions
How many blocks does a bag of mortar lay?
A standard 80 lb bag of mortar mix lays roughly 30 to 35 standard 8x8x16 blocks, or about 120 to 140 standard bricks. This calculator uses about one bag per 33 blocks and one bag per 125 bricks as a working estimate.
How much sand do I need for mortar?
If you mix your own mortar from masonry cement and sand, plan on roughly one ton of masonry sand for every eight to nine bags of cement. Pre-blended bagged mortar mix already contains the sand, so you do not add any.
What mortar type should I use?
ASTM C270 defines mortar types by strength. Type N is the general-purpose choice for above-grade walls, Type S is stronger for below-grade and load-bearing work, and Type M is the strongest for foundations and retaining walls. Match the type to your wall, not just the price.
Does the joint size change the mortar amount?
Yes. Thicker joints and rougher, more absorbent units use more mortar. The estimates here assume a standard 3/8-inch joint; very thick joints or heavy waste can push usage 10 to 20 percent higher.
Sources & references
This tool uses standard formulas and reference values from:
- • American Concrete Institute — ACI 318, Building Code Requirements for Structural Concrete. concrete.org
- • ICC — International Residential Code (IRC), span, footing and framing tables. codes.iccsafe.org
- • APA – The Engineered Wood Association, allowable span and load guidance.
Estimates for planning only. Span, load and code values vary by jurisdiction — verify against your local adopted code and a licensed engineer before building.