Concrete Block Calculator
Enter your wall dimensions to estimate the number of concrete blocks (CMU) and bags of mortar needed, based on standard 16×8 inch block coverage.
Results
- Blocks needed
- 199 blocks
- Mortar bags (approx.)
- 7 bags
- Wall area
- 160 sq ft
Estimates only. Round up and buy a little extra to account for waste, spills, and breakage.
Laying a foundation stem wall, garage wall, or retaining course in CMU? This block calculator converts wall length and height into block count, mortar bags, and the grout or fill you need if the cores are to be filled.
Standard 8 × 8 × 16 in block includes the mortar joint in its nominal size, so each block covers exactly 0.888 sq ft of wall face, or 1.125 blocks per square foot.
Also used as a cinder block calculator, CMU calculator, concrete block wall estimator, and block-and-mortar calculator.
How to use the concrete block calculator
- Enter the wall length in ft.
- Enter the wall height in ft.
- Enter the openings to subtract in sq ft.
- Enter the waste factor in %.
- Optionally add a price to estimate the total project cost.
- Read your quantities instantly — no sign-up, and you can print the estimate to take to the supplier.
Worked example
Inputs
- Wall length
- 20 ft
- Wall height
- 8 ft
- Openings to subtract
- 0 sq ft
- Waste factor
- 10 %
Results
- Blocks needed
- 199 blocks
- Mortar bags (approx.)
- 7 bags
- Wall area
- 160 sq ft
Using the example values above, the concrete block calculator returns 199 blocks (blocks needed). Change any field to match your own project and the numbers update instantly.
How many blocks per square foot?
Nominal 8 × 16 in block face covers 0.89 sq ft, so multiply wall area by 1.125 to get block count. A 40 ft long, 8 ft high wall is 320 sq ft, or about 360 blocks before waste.
Course counting is often easier on site: an 8 in high block plus joint is exactly one course per 8 in of wall height, so a 8 ft wall is 12 courses, and each course is length in inches divided by 16.
Mortar and core fill
Budget about 3 bags of mortar per 100 standard blocks. Cold or windy days and rough block faces increase consumption, so round up rather than stopping mid-course.
If the cores are grouted, a standard 8 in block takes roughly 0.011 cubic yards of grout per block when every core is filled, so 100 fully-grouted blocks need a bit over a cubic yard. Filling every other core roughly halves that.
How much extra should I order?
Always order a little extra. A 5% waste factor suits simple, square projects; 10% is right for most jobs; bump it to 15–20% for irregular shapes, diagonal patterns, or uneven ground. Running short almost always costs more than the leftover material.
Formula
Blocks = wall area × 1.125 (per sq ft for 16×8 block), × (1 + waste%). Mortar ≈ 1 bag per 30 blocks.
Frequently asked questions
- How many concrete blocks per square foot?
- A standard 16×8 inch CMU covers about 0.89 sq ft, so you need roughly 1.125 blocks per square foot of wall.
- How much mortar for a block wall?
- Plan about one 80 lb bag of mortar mix for every 30–35 standard blocks laid.
- How many blocks do I need for a 10x10 wall?
- A 100 sq ft wall takes about 113 standard 8 × 8 × 16 in blocks, so order 120 to cover cuts and breakage.
- How many bags of mortar per 100 blocks?
- About 3 bags of type S or type N mortar mix for standard 3/8 in joints.
- How much does a concrete block weigh?
- A standard 8 × 8 × 16 in block weighs about 35 lb; lightweight versions run closer to 28 lb and solid-filled units far more.
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