Concrete Block Calculator
Enter your wall dimensions to get CMU block count, mortar bags, grout fill volume, and total material cost — with door and window deductions.
How the concrete block calculator works
- Wall area = length × height. Deduct doors and windows from the gross area to get net area.
- Block face area includes the mortar joint. A standard 8×8×16 block covers 0.889 sq ft (8" × 16" = 128 sq in) with its joint.
- Block count = net area ÷ block face area, rounded up. Add 10% waste for cuts and breakage.
- Mortar bags — 1 bag of 60-lb type S mortar covers approximately 25 standard blocks.
- Grout fill — toggle on if you need to fill the hollow cores, common in structural or below-grade walls. The calculator uses a 46% void fraction for 8×8×16 blocks.
Common concrete block sizes
| Nominal Size | Face Area (w/ joint) | Blocks per 100 sq ft | Common Use |
|---|---|---|---|
| 8×8×16 in | 0.889 sq ft | 113 | Foundation, retaining walls, standard CMU |
| 8×8×8 in | 0.444 sq ft | 225 | Half blocks, corners, closures |
| 4×8×16 in | 0.889 sq ft | 113 | Interior partition walls |
| 12×8×16 in | 0.889 sq ft | 113 | Heavy structural walls |
Frequently asked questions
Blocks per 100 sq ft — quick reference
| Block Size | With 10% waste | Mortar Bags | Common Use |
|---|---|---|---|
| 8×8×16 in (standard) | 124 | 5 | Foundations, retaining walls |
| 8×8×8 in (half) | 248 | 5 | Corners, closures, low walls |
| 4×8×16 in (partition) | 124 | 5 | Interior non-load bearing walls |
| 12×8×16 in (wide) | 124 | 6 | Heavy structural walls |
Mortar type: use Type S for below-grade and exterior walls; Type N for interior or above-grade non-structural walls.