One block per square foot runs every wall short

A standard 8x16 block covers 1.125 blocks per square foot, not 1. The block's real face is 128 sq in, or 0.889 sq ft, and 1 ÷ 0.889 is where the 1.125 comes from.

Take a 20 ft by 4 ft wall, 80 sq ft. At 1.125 blocks per sq ft with 10% waste, that is 80 × 1.125 × 1.10 = 99 blocks, rounded up.

Figure it the easy way, one block per square foot, with the same 10% waste, and the same wall comes out to 88 blocks. That is 11 short on an 80 sq ft wall.

Scale it to a one-car garage wall, 200 sq ft at the same 10% waste: 200 × 1.125 × 1.10 = 247.5, rounded up to 248 blocks. The one-block guess calls for 220, a 28-block gap.

Mortar follows the block count, not the square footage. The calculator divides total blocks by 12 and rounds up. At 248 blocks that is 21 bags (248 ÷ 12 = 20.67, rounded up); the 220-block guess would only call for 19.

Check your own wall

Enter the length, height and waste percentage, and the block calculator returns the block count and the mortar bags to match, rounded the way the yard will round them.