Estimate how many standard concrete blocks you need for a wall from its dimensions, with a waste factor.
blocks = wall_area_ft² × 1.125 × (1 + waste)
A standard 16×8″ nominal concrete block covers 0.888 ft² of wall, so you need about 1.125 blocks per square foot.
CMU is dimensionally regular and cut less often, so a 5% waste factor is usually enough.
A foundation wall 40 ft long and 4 ft high is 160 square feet of face. Standard 16 x 8 inch block covers 0.888 square feet each, so you need about 180 blocks before waste. CMU is dimensionally regular and cut far less than brick, so 5% waste is usually plenty — about 189 blocks.
Don't forget the mortar: at roughly 1 bag per 13-15 blocks, 189 blocks needs about 13-14 bags of mortar. Use the mortar calculator to confirm.
Block coverage assumes a 16×8″ nominal face per ASTM C90 sizing. The 1.125 blocks/ft² figure is an industry convention.
A standard 8×8×16-in concrete block covers about 1.125 square feet of wall face including the mortar joint, so the wall area times 1.125 gives the block count before waste. Half blocks, corner blocks, and bond-beam units are counted separately where the design calls for them — they do not change the field count but add to the order.
Block walls need mortar for the joints (roughly 3 bags per 100 block as a planning figure), and structural walls add vertical rebar and grout in the cells. If the design calls for filled cells, estimate the grout volume from the number of filled cores times the cell volume — this can add significant material on a reinforced wall.
About 1.125 for standard 16×8″ nominal block.
About 1.125 standard 8×8×16-inch blocks per square foot of wall, including the mortar joint, so multiply wall area by 1.125 and round up.
Budget roughly 3 bags of mortar per 100 standard blocks. Wider joints or non-standard block sizes shift this figure.
Structural and load-bearing walls often require vertical rebar and grout-filled cells. Estimate the grout from the number of filled cores times the cell volume, which can add considerable material.