Concrete Block Calculator
Figure out exactly how many CMU or cinder blocks you need for a wall, plus mortar and concrete fill estimates.
Wall Dimensions
Estimation Results
Concrete Block Formula
Standard 816 block = 0.889 sq ft of wall area per block
Blocks needed = Wall area 0.889
For estimation purposes only. Verify structural calculations with a licensed engineer.
Concrete Block Estimator: CMU vs Cinder Block
When building a foundation, retaining wall, or partition, you need a highly accurate concrete block calculator to determine material requirements. In the masonry world, you will hear the terms "concrete block", "cinder block", and "CMU block" used interchangeably.
Technically, a CMU (Concrete Masonry Unit) is the modern standard. Older "cinder blocks" were made using coal cinders and were significantly lighter and weaker. Today, almost all structural blocks sold are heavy, high-strength CMU blocks. Our cmu block calculator works perfectly for all standard masonry units because they share the same nominal dimensions.
How to Calculate Concrete Blocks for a Wall
If you are acting as your own cinder block calculator, you can calculate the number of blocks needed manually using a very simple ratio: how many blocks per square foot?
The nominal dimension of a standard 8-inch block (including the standard 3/8-inch mortar joint) is 8 inches high by 16 inches long. This perfectly equals 128 square inches (0.89 square feet) of wall surface area.
Because 1 divided by 0.89 is 1.125, the magic number for any block wall estimator is 1.125 blocks per square foot.
Step 1: Length (ft) × Height (ft) = Total Square Footage
Step 2: Square Footage × 1.125 = Total Blocks
Step 3: Total Blocks × 1.05 = Final order with 5% Waste
For example, if you are building a 20-foot long by 6-foot high wall: 20 × 6 = 120 sq ft. Multiply 120 by 1.125, and you need exactly 135 blocks. Add 5% for waste, and you should order 142 blocks. Our concrete block wall calculator does all of this math instantly.
Cmu Block Fill Calculator (Concrete & Mortar)
When building a structural cmu block wall, you can't just calculate the blocks—you also need to calculate the mortar to hold them together and the concrete to fill the cores (cells). Our tool also functions as a block fill calculator and a mortar estimator.
- Mortar Estimate: One standard 80lb bag of pre-mixed mortar (Type S or Type N) will lay approximately 35 to 40 standard blocks.
- Concrete Core Fill Estimate: If you are pouring solid cells with rebar for maximum structural integrity, you will need a cinder block concrete fill calculator. It takes approximately 1 cubic yard of concrete (or grout) to fill 105 standard 8-inch blocks.