Concrete Block Calculator
Calculate how many concrete blocks (cinder blocks) and mortar bags you need for a wall from its length and height.
ft
ft
in
in
in
%
Adjust based on your mortar mix and joint size.
Results
Blocks Needed
185
Wall Area
160.0 sq ft
Blocks Before Waste
169
Mortar Bags Needed
6 bags
How to Calculate Concrete Blocks Needed for a Wall
This calculator is for concrete block (cinder block) wall construction, not poured or mixed concrete. It divides the total wall area by the face area of a single block — including the mortar joint around it — to find how many blocks the wall requires, then adds a waste allowance for cutting and breakage. It also estimates the mortar bags needed using a standard rule of thumb of about 3 bags per 100 blocks.
Example
A 20 ft long, 8 ft high wall (160 sq ft) built with standard 16" × 8" blocks and a 3/8" mortar joint has an effective block face of about 1.36 ft × 0.7 ft = 0.95 sq ft, so it needs roughly 168 blocks before waste, or about 185 blocks with a 10% allowance — and around 6 bags of mortar mix.
Common Use Cases
- Estimating block quantities for a foundation, retaining wall, or garden wall.
- Getting a materials list together before requesting a quote from a mason or supplier.
- Comparing costs between different standard block sizes for the same wall.
FAQs
How is this different from the site's Concrete Calculator?
The Concrete Calculator and Concrete Slab Calculator are for poured or mixed concrete — they calculate wet concrete volume and cement bags for slabs, footings, and columns. This tool is specifically for concrete block (cinder block) construction, where you're counting individual masonry units and mortar for a block wall, not pouring a volume of concrete.
What's a standard concrete block size?
The most common standard block is nominally 16" long × 8" high × 8" deep, though the actual block is slightly smaller (about 15⅝" × 7⅝") to allow for a 3/8" mortar joint on each side, which is why this calculator adds the joint back in when sizing the effective coverage area.
How much waste should I allow for?
A 5-10% allowance is typical to cover cut blocks at corners and openings, plus breakage during handling. Complex layouts with lots of openings or corners may need a higher allowance.