Concrete Block Calculator
Build a block wall and the two numbers that matter are how many blocks and how many bags of mortar, get either wrong and you're back at the supply yard mid-pour. Enter your wall's length and height below. The calculator counts standard blocks, estimates the mortar, adds a waste allowance, and gives you a cost, so you can buy the whole job in one trip.
How this is calculated
A standard concrete block has a 16 by 8 inch face, which covers about 0.89 square feet of wall once you count the mortar joint. That works out to roughly 1.125 blocks for every square foot. Multiply your wall's length by its height for the total face area, then multiply by 1.125 for the block count. Mortar runs about 3 bags per 100 blocks for standard joints. The tool adds about 5% for breakage and cuts, because some blocks always crack or need trimming at the ends.
A worked example
A wall 40 feet long and 8 feet high is 320 square feet of face. Multiply by 1.125 and you need about 360 blocks. Add 5% for breakage and you're buying around 380. Mortar at 3 bags per 100 blocks puts you near 11 bags. The calculator lands all three the instant you enter the wall size.
Common questions
Multiply your wall's length by its height to get square feet, then multiply by 1.125, since each standard block covers about 0.89 square feet of wall face with the joint. Enter your dimensions above and it's done, waste included.
About 3 bags of mortar mix per 100 blocks for standard 3/8-inch joints. Wider joints or rough block use more. The tool estimates bags from your block count.
Nominally 16 by 8 by 8 inches, which includes the mortar joint; the actual block is slightly smaller. That nominal 16 by 8 inch face is what the 1.125-blocks-per-square-foot figure is based on.
Yes, about 5%. Blocks crack, corners need cuts, and a few always arrive chipped. Running out mid-wall costs you a trip and a delivery fee.
Estimates for planning. Verify against your supplier's units and your local building codes before ordering or building. For anything structural, follow your engineer or local code.