Concrete Block Calculator
Standard 8×16-inch block faces cover just under a square foot each, so block math is nearly one block per square foot — plus waste and mortar. Runs 100% in your browser.
Concrete Block Calculator
About this concrete block calculator
Concrete masonry units (CMU, usually just called concrete blocks) are sized so the math stays simple: a standard 8×8×16-inch block has a face of 128 square inches, and once the 3/8-inch mortar joint is counted in the nominal size, it works out to 1.125 blocks per square foot of wall. Multiply wall area by 1.125, add waste, and you have the order.
Waste covers cut blocks at corners, ends, and around openings — plus the occasional block that cracks when you look at it wrong. Ten percent is the standard allowance; use 15% for walls with many corners or openings, and remember that half-blocks for running bond are cut from full blocks, not bought separately.
Mortar runs roughly one 80-lb bag per 35 blocks for standard blockwork. That covers bed and head joints at normal thickness; thicker joints or sloppy blockwork drink more. If your wall is structural — foundation, retaining, or load-bearing — the block count is the easy part: reinforcement, grout fill, and footing design need engineering, and this calculator does not do that.
How to use
- Measure your wall length and height in feet.
- Choose your block size (standard 8×8×16 in is the default).
- Pick a waste allowance — 10% for straight walls, 15% for corners and openings.
- Optionally enter the price per block, then press Calculate.
Good to know
- Counts full blocks only — half-blocks for bond patterns are cut from full blocks on site.
- Mortar estimate (~35 blocks per 80-lb bag) is a planning figure; joint thickness and block absorption vary it.
- Structural walls (foundations, retaining walls, load-bearing) need engineering for reinforcement and grout — this is a quantity tool only.
Frequently asked questions
How many concrete blocks do I need for a 10x8 wall?
A 10×8 ft wall is 80 sq ft × 1.125 blocks per sq ft = 90 blocks exact — order 99 with a 10% waste allowance, plus 3 bags of mortar.
How many blocks per square foot?
1.125 standard 8×8×16-inch blocks per square foot of wall (face area plus mortar joint). Jumbo 8×8×24-inch blocks run 0.75 per square foot.
How much mortar do I need for concrete blocks?
Roughly one 80-lb bag of mortar per 35 blocks. A 99-block wall needs about 3 bags.
Do I need half blocks?
For running bond patterns, yes — but they are cut from full blocks on site, not ordered separately. Your waste allowance covers the cutting.
Can I build a structural block wall with this calculator?
The count works, but structural design does not come from a calculator: reinforcement, grout fill, and footings for foundation or retaining walls need an engineer and must meet local code.