Free Concrete Block Calculator
Enter your wall dimensions to get the number of concrete blocks, 80-lb mortar bags, and coursing details. Handles standard 8x8x16 block and half-high block, with a waste allowance built in.
This free concrete block calculator takes wall length, height, block size, and openings, then returns the block count with waste, the number of 80-pound mortar bags, and the coursing layout.
Total area of everything the wall does not cover, subtracted before counting.
Estimates for planning and ordering, not engineering advice. See Terms of Use.
How many concrete blocks do you need?
Start with the wall, not the block. Multiply the wall length by the wall height, both in feet, to get the gross square footage, then subtract the area of any doors, windows, and other openings. A standard concrete block (nominal 8x8x16) covers about 0.89 square feet of wall face, because the 3/8 inch mortar joint is included in the nominal size. Divide your net wall area by 0.89 and you have the block count before waste.
Never order the exact count. Blocks break in transit, get cut at corners and openings, and a few always arrive chipped, so add a waste factor. Ten percent is the standard allowance for a simple rectangular wall; use 15% for walls with many corners, angles, or openings that need cutting. Round up at the end, because you cannot buy a fraction of a block, and a second delivery costs more than a few spare blocks.
Coursing matters too. Divide the wall height in inches by 8 for the number of courses (standard block), rounding up, and divide the wall length in inches by 16 for blocks per course; multiply the two for a second route to the same total. If your wall height is not a multiple of 8 inches, the top course will need cutting or a bond beam, so plan for that before you order.
Mortar comes next. A rough rule is one 80 pound bag of Type N mortar for every 35 standard blocks, and this calculator applies that ratio to your final count with the waste already included. For big jobs, confirm with your supplier, because sand-heavy mixes and hot weather change the yield.
Concrete block calculator questions
How many concrete blocks do I need for a 10x10 wall?
A 10 by 10 foot wall needs about 120 standard 8x8x16 blocks before waste: 8 blocks per course times 15 courses. With a 10% waste allowance, order 132 blocks. Subtract any door or window openings first.
What is the standard concrete block size?
The standard concrete masonry unit is 8x8x16 inches nominal, which includes the 3/8 inch mortar joint. The actual block measures about 7-5/8 by 7-5/8 by 15-5/8 inches. Half-high blocks are 8x4x16 inches nominal.
How much mortar do I need per concrete block?
A rough rule is one 80-pound bag of Type N mortar for every 35 standard 8x8x16 blocks. For large jobs, confirm with your supplier, since sand-heavy mixes and hot weather change the yield.
Should I count corners and ends separately?
No, the coursing math covers corners automatically. The 10% waste allowance absorbs the blocks you cut at corners, ends, and openings. For walls with many corners or angles, raise the waste allowance to 15%.