CMU BLOCK
CMU BLOCK COUNT
blocks = ft² ÷ 0.889
ft
ft
ft²
RESULT
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FILL IN ABOVE
1.125 blocks/ft² (8×8×16 face). 5% waste. Mortar = 3 × 80-lb bags per 100 blocks. Estimate only — verify structural designs with engineer.
About this calculator
This CMU calculator estimates the number of concrete masonry units (blocks) for a wall, plus the mortar bags and optional rebar runs. The math assumes standard nominal sizes — face dimension 16" × 8" with a 3/8-inch mortar joint, giving 1.125 blocks per square foot of wall (about 0.889 ft² per block face). Mortar adds three 80-lb bags of Type S per 100 blocks. Rebar follows the IRC and IBC pattern of #4 vertical at 4 ft on center plus #4 horizontal in every fourth course bond beam — typical for non-engineered residential and light commercial. ESTIMATE ONLY — for engineered or load-bearing CMU walls verify with a structural engineer.
Common questions
How many concrete blocks per square foot?
1.125 blocks per square foot of wall using standard 8×8×16 face dimensions with a 3/8" mortar joint — that's 0.889 ft² per block face. A 100 ft² wall needs 113 blocks; round up 5% for breakage and you order 119. Smaller faces (4×16 half-high block, for example) double the block count because the face is half the height.
How many bags of mortar for 100 concrete blocks?
Three 80-lb bags of Type S or N mortar per 100 blocks — about 0.5 ft³ of mortar per 100 blocks at a 3/8 in joint. Type S is the standard for load-bearing CMU walls (1,800 psi compressive strength). For below-grade foundations or seismic regions, the engineer may spec Type M (2,500 psi). Add 10% waste for spillage and partial bags.
When does a CMU wall need rebar?
Per IRC R606 and IBC Chapter 21, every CMU wall in seismic zones D1/D2 needs vertical reinforcement. Most jurisdictions also require rebar for any retaining wall, basement wall, or wall over 8 ft tall. Typical pattern is #4 vertical at 4 ft on center grouted into the cells plus #4 horizontal in every fourth course bond beam. For engineered designs (tall walls, heavy loads, seismic), a structural engineer specifies bar size and spacing — the calculator's rebar option assumes the standard non-engineered residential pattern.