How the calculation works
Units = net wall area ÷ [(actual length + joint) × (actual height + joint)], using consistent units. Apply allowance and round up.
A worked example
A 100 ft² wall with an 8 × 16 in nominal face needs 112.5 block equivalents before waste, or 119 whole blocks with a 5% allowance.
How many blocks per square foot?
A standard block has an 8 × 16 inch nominal face, which is 128 square inches including the mortar joint. That is 1.125 blocks per square foot of wall, or 112.5 blocks per 100 square feet, before allowance. Nominal 4-, 6-, 8-, 10- and 12-inch-wide blocks usually share this face size, so width changes weight and fill, not the count.
| Wall area | Blocks before allowance | With 5% allowance |
|---|---|---|
| 50 ft² | 56.25 | 60 |
| 100 ft² | 112.5 | 119 |
| 200 ft² | 225 | 237 |
| 400 ft² | 450 | 473 |
| 800 ft² | 900 | 945 |
Cinder block or concrete block?
Most people searching for a cinder block calculator mean ordinary concrete masonry units (CMUs). The count works the same way: it depends on the face size and joint, not the name. See cinder block vs concrete block for what to check when buying.
Plan the delivery weight too. One manufacturer, Basalite, lists its standard 8 × 8 × 16 unit at 40 lb, so 119 of those blocks weigh about 4,760 lb before the pallet. See concrete block weight for other sizes. For landscape walls built from stacking units, use the retaining wall block counter; for brick veneer, use the brick calculator.
How many standard blocks cover 100 square feet?
An 8 × 16 inch nominal face module requires 112.5 block equivalents for 100 square feet. With a selected 5% purchase allowance, round up to 119 blocks. Openings, corners and special units can change the order.
Should I enter nominal or actual block dimensions?
Enter actual face dimensions and the joint width separately. For a common nominal 8 × 16 inch module, actual 7⅝ × 15⅝ inch faces plus ⅜ inch joints form the module. Do not add a joint to nominal dimensions again.
What to check before using the result
- Nominal dimensions include the joint module; actual face dimensions do not.
- Thickness is not the block face area. Count corners and special units separately.
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References & product information
- CMHA: Modular Layout of Concrete Masonry
- QUIKRETE Mason Mix #1136 data sheet
- Basalite: Building Blocks product sheet (unit weights)
Method prepared 2026-10-21. See our calculation and editorial methods. Spotted a problem? Tell us about it.