Concrete Block Calculator
Find how many concrete blocks (CMU) a wall needs, less doors and windows, with the mortar and sand to lay them and the cost.
Change the values and press Calculate to work out your own figures.
Enter the wall's length and height and choose the block size.
Show the working
- blocks = (wall area − openings) ÷ block face area, rounded up
- mortar: about 12 blocks per 80 lb bag; site-mixed, 3 bags of cement per 100 blocks and 1 cu yd of sand per 7 bags
How to use it
Enter the wall's length and height and choose the block size.
Lengths can be decimals, fractions or tape entries such as 12' 6 1/2" (in feet or inches). Prices are optional.
Key facts
blocks = (wall area − openings) ÷ block face area, rounded up an 8 × 16 in face is 8/9 sq ft, so 1.125 blocks per sq ft
Sizes
Block sizes are nominal: an 8 × 8 × 16 block is 7⅝ × 7⅝ × 15⅝ in, and the 3/8 in mortar joint makes up the rest.
Mortar
An 80 lb bag of premixed mortar lays about 12 blocks; site-mixed, allow about 3 bags of cement and 3/7 cu yd of sand per 100 blocks.
Questions
How many blocks for a 20 × 8 ft wall?
180 standard 8 × 16 in blocks (160 sq ft × 1.125).
How many blocks per square foot?
1.125 standard blocks.
Formulas
blocks = (wall area − openings) ÷ block face area, rounded up an 8 × 16 in face is 8/9 sq ft, so 1.125 blocks per sq ft
Sources
Limitations
- Material densities are typical values (the midpoint of the commonly published range); real loads vary with moisture, grading and compaction, so check with your supplier or type in their density.
- Tank results are the geometric volume; real tanks have wall thickness and fittings.