A standard concrete block (CMU) has a nominal 16×8-inch face, so with mortar joints you need about 1.125 blocks per square foot of wall. This calculator takes the wall length and height, applies a waste allowance, and estimates both the block count and the mortar bags.
Reviewed: June 20, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: standard CMU coverage, recomputed in code.
How it's counted
The 1.125 comes from the block face: 16 × 8 inches is 0.889 ft², and one divided by 0.889 is 1.125 blocks per square foot once the mortar joints are included. The wall area is length times height. A waste allowance of 5–10% covers cutting at corners and breakage. Mortar is estimated at roughly three bags per hundred blocks, which varies with joint thickness.
Worked examples
20 ft × 8 ft wall, 10% waste:
30 ft × 10 ft wall, 5% waste:
12 ft × 8 ft wall, 10% waste:
For a wall with a doorway, compute the door's area (say 3 ft × 7 ft = 21 ft²), multiply by 1.125 to get about 24 blocks, and subtract those from the total. The waste allowance still applies to the net wall area.
Frequently Asked Questions
~1.125 per ft². 20×8 ft (160 ft²) ≈ 180, or 198 with 10% waste.
About 1.125 for 16×8-inch blocks (each face ≈ 0.889 ft²).
~3 bags per 100 blocks. 200 blocks ≈ 6 bags.
5–10% for cutting, corners and breakage.
No — deduct an opening's area × 1.125 yourself for large doors/windows.