Block count formula
Nominal sizes include the ⅜ in mortar joint. An "8 × 8 × 16" block is actually about 7⅝ × 7⅝ × 15⅝ in, so using the nominal face size already allows for the joints.
Worked example: 40 ft wall, 4 ft tall, 8 × 8 × 16 block
- Wall area: 40 × 4 = 160 ft².
- Block face: 16 × 8 ÷ 144 = 0.889 ft².
- Blocks: 160 ÷ 0.889 = 180.
- With 5% waste: 180 × 1.05 = 189 blocks.
- Core fill at 0.23 ft³ per block : 180 × 0.23 = 41.4 ft³ = 1.53 yd³.
Concrete block fill calculator
Reinforced block walls have grout or concrete in the cells that hold rebar, and sometimes in every cell. Switch the calculator to Core fill. Set the fill per block and the share of cells filled. For example, 50% if every other cell is grouted. The result gives yards and bag counts.
Fill per block depends on the core size, which varies by manufacturer and block type. The defaults are planning estimates. Check the block maker's data sheet . Grout for reinforced masonry may need a specific mix, such as a fine or coarse grout, rather than standard bagged concrete.
Mortar
Mortar coverage depends on bag size, joint thickness, and mortar type. The calculator uses blocks per bag, which you can edit. Read the mortar bag for its figure .
Before the first course
- Block walls sit on a concrete footing. Size its volume with the concrete footing calculator.
- Pouring the wall instead of laying block? Use the concrete wall calculator.
- For a full takeoff of footings, slabs, and piers, use the main concrete calculator.
Quantity estimate only. Reinforcement, grout spacing, and wall height limits come from your plans, local code, or an engineer.