This mortar calculator for block walls estimates laying mortar from a known CMU count and a product coverage or documented batch yield. Use it for concrete block, cinder block and cement block projects. Sand and cement quantities need the exact site mix recipe, including any lime or other specified ingredients, rather than a universal cement to sand ratio.
Maintained by BlockCalculatorPro. Check our reference cases.
How this calculator works
Premixed bags = installed block equivalents ÷ documented blocks per bag × (1 + mortar allowance ÷ 100), rounded up. Recipe mode scales the ingredients in your supplied batch.
Coverage must match the unit, joints and bedding. Mortar for laying blocks is separate from core fill grout.
First identify what is inside the bag
| Material | What to check | What the estimate covers |
|---|---|---|
| Premixed sanded mortar | Coverage for the selected bag size and unit | Mortar used to lay the blocks |
| Masonry cement or mortar cement | Required sand and manufacturer batching directions | An ingredient in a site mixed mortar |
| Core fill masonry grout | Mixed volume yield and project specification | Specified hollow cells and channels |
A bag of masonry cement is not a complete sanded mortar mix. Portland cement alone is also an ingredient, rather than a ready to use laying mortar. Check the product label before entering coverage or pricing the order.
The calculator estimates quantities for your selected material. Mortar type must follow the project requirements and manufacturer guidance. A coverage example is not a recommendation to use that mortar type in every wall.
Estimate premixed mortar bags from block coverage
Unrounded bags = installed blocks ÷ blocks per bag × (1 + waste percentage ÷ 100). Round up once at the purchasing step. Keep the selected bag weight and product coverage together.
QUIKRETE's Mortar Mix data sheet states that one 80 lb bag lays up to 13 standard 8 × 8 × 16 blocks. This is a product specific coverage statement. It does not establish the yield of all 80 lb mortar bags, every block shape or every bedding method.
For 180 installed standard blocks with that coverage and a chosen 5% mortar allowance: 180 ÷ 13 × 1.05 = 14.5385 bags. The purchase estimate is 15 bags. The 5% allowance is an example input. Actual waste can differ with joint size, working conditions and interruptions.
Use installed blocks rather than every spare you buy
A wall might contain 180 blocks while its block order is 189 units after a 5% breakage allowance. Normally, mortar should begin with the 180 units being laid and then receive its own allowance. Starting from 189 and applying another 5% would combine two different allowances.
Count special units separately if they require a materially different joint pattern. Deduct masonry openings when deriving the installed count from wall area. A rough area takeoff cannot predict every cut or the exact number of corner and bond beam units.
Bag coverage depends on more than block width. Bed and head joint thickness, face shell bedding, full bedding and the initial leveling bed can affect consumption. Use coverage that matches the work or replace it with a measured yield from the same job conditions.
Calculate sand and cement from a documented batch
For a site mixed mortar, obtain both the specified ingredient quantities per batch and the number of blocks laid by that batch. A ratio without a practical yield is insufficient for a dependable material order.
Required batches = installed blocks ÷ blocks per documented batch × (1 + allowance percentage ÷ 100). Multiply that batch quantity by each recipe ingredient. Keep cement bag quantities, sand volume and any other ingredients in their original units until conversion is needed.
For an arithmetic example, suppose an approved job recipe uses one cement bag and 0.10 cubic metre of sand per batch, includes any other ingredients required by that recipe, and a trial batch lays 40 blocks. For 100 blocks and an 8% allowance, the requirement is 2.7 batches. This represents 2.7 cement bags and 0.27 cubic metre of sand, plus the proportionate amounts of every other recipe ingredient. Buying whole cement bags would require three bags. These illustrative inputs do not prescribe a mortar formulation.
If only whole batches can be produced, round the batch count up before multiplying all ingredients. Otherwise, preserve the fractional calculation and round each purchase unit at the end. Do not apply a generic dry to wet volume multiplier or convert sand volume to weight without a suitable density.
Compare the full mortar order
- Check the selected product, mortar type, bag size and published coverage.
- For site mixing, include sand, cement, lime or other recipe ingredients and their delivery charges.
- Compare bagged mortar with site mixed materials using the same installed quantity and waste assumptions.
- Keep core grout and footing concrete outside the laying mortar line.
- Use local quotes for material cost. Mixing labor, storage and handling can change the cheaper choice.
CMHA identifies batching, unit tolerances, construction conditions and work stoppages as sources of variation in mortar consumption. A measured site yield can therefore be more useful than an apparently precise generic rule.
Common questions
How many concrete blocks does a bag of mortar lay?
Use the coverage for the exact product and bag size. For example, QUIKRETE Mortar Mix lists up to 13 standard 8 × 8 × 16 blocks per 80 lb bag. Actual coverage depends on the joint and bedding conditions. Other mortar products can have different coverage.
How much mortar is needed for 100 blocks?
At the named coverage of 13 blocks per 80 lb bag, 100 blocks require about 7.69 bags before allowance. With a chosen 5% allowance, the figure is about 8.08 bags, so buy nine whole bags. Confirm the product and actual coverage before ordering.
How do I calculate cement and sand for a block wall?
Use the specified site mix recipe and its documented blocks per batch. Calculate the required batches, then multiply by the cement, sand and every other ingredient per batch. The block count alone cannot establish an appropriate cement to sand ratio or mortar type.
Are masonry cement and premixed mortar the same?
No. A sanded premixed mortar already includes its aggregate. Masonry cement generally requires masonry sand under the manufacturer's batching directions. Their bag counts cannot be substituted directly.
Can I use mortar coverage to estimate grout for CMU cells?
No. Laying mortar coverage describes joints between blocks. Core grout is estimated from the cavity volume and the specified filling pattern, then divided by the selected grout product's mixed yield.
Can I scale 80 lb coverage directly to a 60 lb bag?
Use the manufacturer's yield for the actual bag size when available. A simple weight ratio is only an assumption if composition and mixed yield per unit mass are equivalent. Do not apply it across different products.
Sources and product references
Named product references support the examples. Confirm the currently supplied dimensions, yields and purchasing conditions before ordering.
- QUIKRETE Mortar Mix No. 1102 product data sheetAn 80 lb bag lays up to 13 standard 8 × 8 × 16 inch units. Use coverage appropriate to the specified unit and bedding conditions. The product is premixed laying mortar, not core grout.
- CMHA: Estimating Concrete Masonry Materials, TEK 04 02ADistinguishes masonry cement mortar, preblended mortar and cement lime mortar, and explains why construction conditions affect consumption.