Cinder Block Calculator
Calculate how many cinder blocks (CMU) you need for a wall from its length and height, using the standard 16x8 in face size, plus cost.
How this calculator works
Whatever you call it — cinder block or CMU — the standard unit measures 16 in x 8 in nominally, giving an exposed face of about 0.888 sq ft. This calculator divides your wall’s total area by that face size to get the block count, rounding up since blocks are sold as whole units.
Formula: Blocks = Wall area (sq ft) ÷ 0.888 sq ft per block.
Worked example
A wall 20 ft long x 8 ft high (160 sq ft):
- Area: 20 × 8 = 160 sq ft
- Blocks: 160 ÷ 0.888 ≈ 180.1802 → rounds up to 181 blocks
- At $2.50/block, that’s $452.50 before waste.
Coverage reference
| Wall area | Blocks needed (~1.125/sq ft) |
|---|---|
| 10 x 4 ft | 46 blocks |
| 20 x 8 ft | 181 blocks |
| 40 x 16 ft | 721 blocks |
How to measure your wall
Measure the wall’s full length and height in feet, entering length in the Length field and height in the Width field. If your wall has door or window openings, subtracting their area gives a tighter count, though the waste allowance usually absorbs small cutouts without extra math — and remember this counts face blocks only, not the mortar or any grout fill needed for reinforced cores.
Frequently asked questions
Is a cinder block the same thing as a concrete block?
For estimating purposes, yes — 'cinder block' is the everyday name most people use for what the masonry trade calls a CMU (concrete masonry unit), and both use the same standard 16 in x 8 in nominal face size in this calculator. You'll get the identical block count either way.
Why is it called a 'cinder' block if it's made of concrete?
The name is a holdover from the material's early history: blocks made from the mid-1900s through about the 1970s often used coal cinders (ash from burning coal) as lightweight aggregate in the concrete mix. Modern blocks use gravel, sand, or expanded shale instead — true cinder aggregate has been essentially obsolete in the U.S. for decades, but the old name stuck.
How many cinder blocks do I need for a wall?
A standard 16 in x 8 in block has an exposed face of about 0.888 sq ft. Enter your wall's length and height in feet and this calculator divides the total area by that face size, rounding up to a whole block.
How much waste should I add for a cinder block wall?
5-10% is typical, covering broken units, cuts at corners and openings, and course heights that don't divide evenly. Walls with several window or door openings, or an odd top-course height, tend toward the higher end of that range.
Are lightweight cinder-era blocks still available, or are all blocks the same weight now?
Standard modern CMUs are heavier than the old cinder-aggregate blocks, but lightweight versions still exist, made with expanded shale, clay, or slate aggregate instead of coal ash. They cost more per block but are easier to lift and offer somewhat better insulation, which matters for taller walls or DIY installs.
Estimates only. Verify quantities with your supplier before purchasing.