Concrete Block Calculator
Count the cinder blocks or CMU needed for a wall, plus the number of courses and blocks per course.
How to use the Concrete Block Calculator
- Enter the wall length and pick its unit.
- Enter the wall height and pick its unit.
- Choose the block face size (nominal).
- Enter the doors & windows area and pick its unit.
- Enter the waste allowance.
- Enter the price per block.
- Press Calculate. The result updates automatically as you type.
About the Concrete Block Calculator
Concrete masonry units (CMU), often called cinder blocks, are named by width × height × length, so an "8 × 8 × 16" is 8 in thick. The wall thickness doesn't change how many blocks cover a square foot, only the weight and the amount of grout if the cores are filled.
Lay out walls in multiples of 8 in for length and height whenever you can to avoid cutting block. Corners, ends and openings use special units such as corner, bullnose and half blocks; the waste allowance roughly covers these, but list them separately when ordering. Reinforced walls also need rebar and core grout per your plans.
Formula
Blocks per sq ft = 144 ÷ (Nominal length × Nominal height)
Blocks = Net wall area × Blocks per sq ft × (1 + waste %)
Courses = Wall height ÷ Block height
Nominal sizes already include a ⅜ in mortar joint: a standard block is actually 15⅝ × 7⅝ in, which becomes 16 × 8 in in the wall. That gives 1.125 blocks per square foot.
Example calculation
Using the default values:
- Wall length = 30 ft
- Wall height = 6 ft
- Block face size (nominal) = 8 × 16 in face (standard 4, 6, 8, 10, 12 in CMU)
- Doors & windows area = 0 ft²
- Waste allowance = 5%
the calculator returns:
- Blocks needed: 213 blocks
- Courses (rows): 9 courses
- Blocks per course: 23 blocks
- Blocks per sq ft: 1.125
Frequently asked questions
How many concrete blocks are in a square foot?
Standard 8 × 16 in blocks cover 0.889 sq ft each, so there are 1.125 blocks per square foot.
How many blocks do I need for a 100 sq ft wall?
About 113 standard blocks, or around 119 with 5% extra for breakage and cuts.
What is the actual size of an 8 × 8 × 16 block?
It measures 7⅝ × 7⅝ × 15⅝ in. The ⅜ in mortar joint brings it to the 8 × 16 in nominal module.
Last updated: · Category: Construction calculators