Concrete Block Calculator
A concrete block calculator tells you how many blocks you need for a wall by dividing the wall area by the face area of one block. A standard block face covers about 1.125 square feet (a nominal 8 by 16 inch face), so divide your wall square footage by 1.125. Enter your wall dimensions below for the block count and mortar estimate.
Standard nominal block face 8x16 in = 1.125 sq ft. Adds ~5 percent waste. Mortar approx 3 bags per 100 blocks.
- Wall area
- 0 sq ft
- Mortar bags
- 0
Enter wall length and height to see how many blocks you need.
Estimate only. Material yields and prices vary by supplier and region; confirm before ordering.
How Do You Calculate How Many Concrete Blocks You Need?
To calculate concrete blocks, find the wall area by multiplying length by height in feet, then divide by the face area of one block. A standard concrete block (CMU) has a nominal face of 8 by 16 inches, which is 1.125 square feet, so a 20 by 8 foot wall of 160 square feet needs about 142 blocks before waste. Add around 5 percent for cuts and breakage. The calculator does this and estimates mortar too.
How Much Mortar Do You Need for Concrete Block?
Mortar usage runs roughly 3 bags per 100 blocks for standard block laid with normal joints, so a 142 block wall needs about 4 to 5 bags. This is an estimate, since joint thickness and your technique change the real figure, so treat it as a starting point and buy a little extra. The calculator gives a mortar estimate alongside the block count so you can order both together.
What Size Is a Standard Concrete Block?
A standard concrete block, also called a CMU (concrete masonry unit), has a nominal size of 8 by 8 by 16 inches, where nominal includes the mortar joint. The actual block is slightly smaller (about 7.625 inches) so that with a 3/8 inch joint it lays out on an 8 inch module. This is why calculations use the nominal 1.125 square foot face: it accounts for the joint automatically.
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Frequently asked questions
- How many concrete blocks do I need for a wall?
- Divide the wall area in square feet by 1.125 (the face area of a standard 8 by 16 inch block), then add about 5 percent for waste. A 160 square foot wall needs roughly 150 blocks with waste.
- How many concrete blocks are in a square foot?
- There are about 0.89 standard blocks per square foot of wall, since each block face covers 1.125 square feet. Multiply your wall area by 0.89 for a quick estimate.
- How much mortar do I need for concrete blocks?
- Plan on roughly 3 bags of mortar per 100 blocks for standard block and joints. Buy a little extra, since joint thickness and technique change the real amount.