Concrete Block Calculator
Count the standard 16-by-8 CMU blocks and mortar bags needed for a wall, from its length and height, with a waste cushion.
How it works
Enter the wall's length and height in feet. The calculator finds the wall face area, then divides by the coverage of one standard concrete masonry unit. A nominal 16-by-8-inch block covers about 0.89 square feet of wall once you account for the mortar joint, which is why a wall never needs quite as many blocks as a naive length-times-height guess suggests.
It then adds your waste percentage for the blocks that crack, get cut down at openings, or just don't survive the pallet, and rounds up to whole blocks. Mortar comes next: as a rule of thumb one 70-pound bag of mortar mix lays roughly 28 blocks, so the bag count is the block count divided by 28 and rounded up.
The result is a quick materials list for a straight, solid run of block. Openings for doors and windows will trim the count a little, and tall or load-bearing walls may need reinforcement and grout the calculator doesn't cover — treat those as separate line items.
Frequently asked questions
How many blocks are in a square foot of wall?
A standard 16-by-8-inch CMU covers 128 square inches, or about 0.89 square feet, once the block sits with its mortar joints. That works out to roughly 1.125 blocks per square foot of wall face, which is the figure the calculator uses before adding waste.
How much mortar do I need?
Plan on about one 70-pound bag of mortar mix for every 28 standard blocks as a working estimate. Cold weather, wide joints, and rough block all push that up, so buy a bag or two extra rather than running out mid-course.
Does this account for door and window openings?
No — it estimates a solid wall, so it slightly overcounts if you have big openings. That's usually fine as a buffer, but for a wall with large doors or windows you can subtract those areas from the length-times-height first.