Block Wall Calculator
Count concrete blocks, mortar and core grout for a block wall. Works for 4", 6", 8" and 12" CMU with grouted cells at any spacing.
How it's calculated
A standard block has a nominal face of 8" × 16", including a 3/8" mortar joint. That is 0.889 sq ft, so a wall takes 1.125 blocks per square foot. The calculator multiplies your net wall area by that and adds waste.
Mortar is figured from the field rule of about 13 blocks per 80 lb bag of pre-mixed mortar, or about 30 blocks per bag of masonry cement mixed with roughly 3 cubic feet of sand.
Core grout uses about 0.26 ft³ per fully grouted 8" block. Grouting cells at 48" on center fills one of every six cores.
Worked example
A 40 ft wall, 4 ft tall, is 160 sq ft. At 1.125 blocks per sq ft plus 5% waste, that is 189 blocks. With cells grouted every 48", you need about 0.30 yd³ of grout, or 14 bags of 80 lb mix.
Field notes
- Plan wall heights in 8" increments. Every partial course means cutting a whole row of block.
- Lay the first course in a full mortar bed on a level footing. Every course above inherits its errors.
- Fill cells that contain vertical rebar, and any cell where a bolt or strap is set.
- Order bond beam and corner blocks separately if the plans call for them.
Common questions
- How many blocks are in a square foot?
- 1.125 for standard 8×8×16 block. A 100 sq ft wall takes about 113 blocks before waste.
- How many blocks per bag of mortar?
- About 13 blocks per 80 lb bag of pre-mixed mortar, or around 30 per bag of masonry cement when you mix your own with sand.
- Do I need to fill block cores with concrete?
- Only cells with rebar, anchor bolts or where the plans require solid grouting. Retaining and foundation walls usually need grouted, reinforced cells.