Concrete Block Calculator
CMU blocks and mortar bags for a wall.
Enter your values
Enter the wall length in ft.
Enter the wall height in ft.
Enter the block width in in.
Enter the block height in in.
Enter the waste allowance in %.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Blocks needed
- 284
- Wall area
- 240 sq ft
- Mortar bags (80 lb, ~33 blocks/bag)
- 9
Quick answer
Block count is wall area divided by the face area of one block, plus waste, and mortar scales with block count.
blocks = ceil(wall area / block face area x (1+waste%))
At a glance
| What it does | CMU blocks and mortar bags for a wall. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Wall length, Wall height, Block width, Block height, Waste allowance |
| Main output | Blocks needed |
| Formula | blocks = ceil(wall area / block face area x (1+waste%)) |
| Cost | Free — no sign-up, no download |
How to use the Concrete Block Calculator
- 1Measure the wall length and height.
- 2Enter the block face dimensions, standard CMU is 16x8 in.
- 3Add 5-10% waste and figure roughly one 80 lb mortar bag per 33 blocks.
Inputs explained
- Wall length(ft)
- Enter the wall length in ft.
- Wall height(ft)
- Enter the wall height in ft.
- Block width(in)
- Enter the block width in in.
- Block height(in)
- Enter the block height in in.
- Waste allowance(%)
- Enter the waste allowance in %.
Worked example
Using the values the calculator loads with:
Inputs
- Wall length30 ft
- Wall height8 ft
- Block width16 in
- Block height8 in
- Waste allowance5 %
Results
- Blocks needed284
- Wall area240 sq ft
- Mortar bags (80 lb, ~33 blocks/bag)9
Frequently asked questions
How many blocks per bag of mortar?
About 33 standard 8x16 blocks per 80 lb bag of mortar, less for thicker joints.
Do I need rebar and grout?
Load-bearing block walls usually need vertical rebar and grouted cores per your local code.
What do I need to enter into the Concrete Block Calculator?
Just 5 values: wall length, wall height, block width, block height, waste allowance. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Concrete Block Calculator work out the answer?
Block count is wall area divided by the face area of one block, plus waste, and mortar scales with block count. It applies the formula blocks = ceil(wall area / block face area x (1+waste%)) and shows the working so you can check each step by hand.
Is the Concrete Block Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.