Concrete Block Calculator
Estimate how many CMU concrete blocks and bags of mortar you need for a wall — from length and height, with deductions for openings and a waste allowance.
How to Use
- Enter the wall length and height in feet to set the gross face area.
- Subtract the total area of any door or window openings in square feet so you do not over-order block.
- Set a waste percentage (10% is typical) to cover breakage, cuts, and culling.
- Read the block count, mortar bags, and how many courses the wall stands.
- Check the step-by-step Show Work below to see every figure.
Show Work
Notes
About the Concrete Block Calculator
Meet the Concrete Block Calculator: a free, no-fuss tool for building, materials estimation and site work with nothing to install and no sign-up. Estimate how many CMU concrete blocks and bags of mortar you need for a wall — from length and height, with deductions for openings and a waste allowance.
How it works
Put each value in its box and read the answer as you go. Because it recalculates live, you can play with the inputs to see how each one moves the result — handy for checking your own working or planning ahead. Everything happens on your device, so it is fast and private.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
How many blocks are in a square foot of wall?
A standard 8" × 8" × 16" concrete block laid with a 3/8" mortar joint covers about 0.89 ft² of wall face, so it takes roughly 1.125 blocks per square foot. This tool uses that 1.125 rate, so just enter your wall dimensions and it does the count for you.
How much mortar does a block wall need?
A common rule is about 3 bags of mortar mix per 100 blocks laid with standard 3/8" joints. This calculator uses that ratio, reporting mortar as 70-lb bags. Wider joints, hollow-core grouting, or rough block faces will push the figure higher.
Why subtract openings?
Doors, windows, and vents remove real wall area. A single man-door is around 21 ft², which is roughly 24 blocks you would otherwise pay for and store. Add up the area of every opening and enter the total so the block and mortar counts reflect what you are actually laying.
How many courses tall is my wall?
A nominal 8"-high block (including the joint) gives one course per 8 inches of height. An 8-ft wall is 96 inches, so it stands 12 courses. The tool reports courses so you can plan rebar, bond beams, and lift heights for your crew.
How much waste should I add?
Plan on about 5–10% extra for a clean, square wall and up to 15% where there are lots of cuts around openings or corners. Ordering a little long leaves matching block on hand for repairs and avoids a second delivery if a few units crack during the lay.
How do I use the Concrete Block Calculator?
Simply type your numbers and read the result, which refreshes the instant you change something. There is nothing to submit and nothing to wait for.
Do I need to install or sign up for anything?
Not at all — it runs in the browser with nothing to install and no account. After it loads once, it even works without an internet connection.
Is my information private?
Yes. Everything happens in your browser. Nothing you type is sent to a server or saved anywhere.
Common Use Cases
Ordering block for a wall
Turn wall dimensions into an exact block count plus a waste cushion so you buy once and skip a second delivery fee.
Budgeting a foundation or stem wall
Get block, mortar bags, and course count up front to price a job before committing to materials.
Planning a wall with openings
Subtract doors and windows so a garage or basement estimate is not inflated by area you will never build.
Estimating a garden or retaining wall
Size a low CMU wall and order the right amount of block and mortar in a single trip.
Checking a contractor quote
Compare a mason’s block quantity against the wall you measured to spot padding before you sign.
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