Concrete Block Calculator
Estimate how many concrete blocks (CMUs) you need for a wall project, including waste and estimated cost.
This concrete block calculator turns your wall's length and height, plus your chosen block size, into an exact block count. Enter your dimensions, pick a standard 8x8x16, 6x8x16 or 4x8x16 block (or enter a custom size), set a waste percentage for cuts and breakage, and optionally add a price per block to get a full material and cost estimate before you order.
Your Estimate
Wall Area
160.0 sq ft
Block Face Area
128.0 sq in
Blocks Needed
180 blocks
Extra Blocks for Waste
18 blocks
Total Blocks to Buy
198 blocks
Estimate assumes a running-bond wall with no door, window or vent openings. Subtract those areas from the wall before ordering.
Results Actions
Block face size drives the count — nominal block sizes include an allowance for mortar joints. Always confirm exact block dimensions with your supplier before ordering.
Common Concrete Block Sizes
How to Use the Concrete Block Calculator
- 1Choose Imperial or Metric measurements.
- 2Enter your wall length and wall height.
- 3Select a standard block size — 8x8x16, 6x8x16 or 4x8x16 — or choose custom to enter your own block dimensions.
- 4Set a waste percentage — 10% is typical for straightforward rectangular walls.
- 5Optionally enter a price per block to see an estimated total cost.
- 6Read your results instantly: wall area, block face area, blocks needed, waste, and total blocks to buy.
Example Calculation
Say you're building a 20 ft long, 8 ft high wall using standard 8x8x16 blocks, with a 10% waste allowance and blocks priced at $2.50 each. Wall area = 20 x 8 = 160 sq ft. Block face area = 8 in x 16 in = 128 sq in. Converting the wall area to square inches (160 sq ft x 144) = 23,040 sq in. Blocks needed = 23,040 ÷ 128 = 180 blocks. Waste at 10% = 18 blocks, for a total of 198 blocks to buy. Estimated cost = 198 x $2.50 = $495.00.
Accuracy & Assumptions
- Results are estimates only and are meant for planning purposes.
- Calculations assume a running-bond wall with no openings for doors, windows or vents — subtract those areas manually.
- Actual block coursing may not divide evenly and could require additional cut blocks.
- Mortar, rebar, grout and wall ties are not included in this estimate and should be calculated separately.
- Verify all wall measurements and consult a professional for structural or load-bearing walls.
Frequently Asked Questions
How is the number of blocks calculated?
We calculate the total wall area from your wall length and height, then divide it by the face area of a single block (height x length). A waste percentage is added on top to account for cuts and breakage, giving you a total to buy.
Does this account for mortar joints?
Standard block sizes (like 8x8x16) are nominal dimensions that already include an allowance for a 3/8 inch mortar joint, so using the nominal size in this calculator gives a realistic block count for typical construction.
What waste percentage should I use?
10% is a reasonable default for straightforward rectangular walls. Walls with lots of corners, curves, or openings for doors and windows may need 15% or more to cover extra cuts.
Does this calculator subtract doors and windows automatically?
No. This calculator estimates blocks for a solid wall area. If your wall has door, window or vent openings, subtract those areas from your total wall area before entering your dimensions, or reduce the block count manually.
What about mortar, rebar and grout?
This calculator only estimates the number of concrete blocks. Mortar, vertical rebar, horizontal reinforcement and grout for filled cores should be calculated separately based on your wall design.
This calculator provides an estimate for planning purposes only. Block sizes, mortar joint widths and wall designs vary by supplier and project — always confirm exact quantities with your mason or supplier before ordering.