Block wall calculator
This divides your wall's face by a block's face and rounds up. It does not judge whether a block wall suits the job, how it should be reinforced or bonded, or what it will bear — those are questions for your plans or an engineer. Confirm the count against the actual wall before you order.
Enter the wall's length and height and the face size of your block, and the tool works out the wall area, divides by the block's face area, adds a little for breakage and rounds up to whole blocks.
Worked example
A wall 20 ft long and 8 ft high is 160 ft². A standard block covers 16 × 8 inches, or 1.125 ft², so 160 ÷ 1.125 = 142 blocks before waste. Add 5% for breakage and cuts and you would buy 150. A taller course count or a different block module shifts that straight away — the tool re-runs it as you edit.
The formula
blocks = (wall area × (1 + waste)) ÷ block face area, rounded up
Wall area is length × height. One block's face area is its nominal length times its nominal height, joint included, so the division already accounts for the mortar lines. The waste covers breakage and the part-blocks at ends and openings.
What this tool assumes
Only that a laid block covers its nominal face — and you set that face size, so even that is editable. The wall area, the block module and the waste are all yours; there is no hidden block table steering the count.
Questions
- How many concrete blocks do I need for a wall?
- Divide the wall face area by the face area of one block. A standard block laid up with its mortar joint covers about 16 inches by 8 inches, which is 128 square inches, or 1.125 ft² over its face — so a wall reads at roughly 1.125 blocks per square foot. Enter your wall size above and the block count, plus a waste allowance, appears as you type.
- What size should I enter for the block?
- Use the nominal face size, mortar joint included — that is the area a laid block actually covers on the wall. A common CMU sits at 16 × 8 inches nominal (about 390 × 190 mm), which is the editable default here. If your block is a different module, type its face length and height and the count follows.
- Do I subtract door and window openings?
- For a tight count, yes — measure the openings and knock their area off the wall area you enter. Many masons leave small openings in and let the waste factor absorb the cut blocks. For a big garage or window opening it is worth subtracting, since that is real blocks you would otherwise buy and stack for nothing.
- Does this include the mortar?
- No — this counts blocks only. Mortar is a separate order that depends on the joint size and the number of blocks, so it lives on its own page. Take the block count from here to the mortar calculator and it will turn it into bags.
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