Calculate how many concrete masonry units (CMU blocks) and mortar bags you need for a wall, based on wall size and standard block dimensions.
Google AdSense Banner
This area will contain advertisements after approval.
Google AdSense Banner
This area will contain advertisements after approval.
This calculator divides the total wall area (plus a waste allowance) by the block's nominal face area: Blocks Needed = (Wall Area × (1 + Waste%)) ÷ (Block Length × Block Height ÷ 144), using nominal dimensions (which already build in a standard mortar joint, unlike raw brick dimensions). This is a completely different calculation from our Concrete Calculator, which estimates poured, mixed concrete by volume for slabs and footings, not discrete block units for a wall.
The default 16 in × 8 in nominal size reflects the most common standard concrete block used in the US, though the actual block (before accounting for the mortar joint) measures closer to 15.625 in × 7.625 in. Always confirm the exact block size you're using, since other sizes (like 4 in or 12 in wide blocks) are also common depending on the application.
For a 20 ft × 8 ft wall using standard 16 in × 8 in nominal blocks and 10% waste: the 'Wall Area' result you see is the raw, pre-waste figure, 20 × 8 = 160 sq ft. Internally, the calculator also works out an area with waste added (160 × 1.10 = 176 sq ft) to determine the block count, but that waste-adjusted number isn't itself shown as a separate result, only the final block count reflects it. Each block's nominal face area is (16 × 8) ÷ 144 ≈ 0.8889 sq ft, so blocks needed = 176 ÷ 0.8889 = 198 blocks exactly. Mortar bags needed = (198 ÷ 100) × 3 ≈ 5.94, rounded up to 6 bags.
Entering the block's actual manufactured size instead of its nominal size, this calculator expects nominal dimensions (which already include the mortar joint allowance), using the smaller actual size would overcount how many blocks are needed.
Confusing this tool with the Brick Calculator, concrete blocks (CMU) are much larger than bricks and use nominal sizing that already bakes in the mortar joint, entering brick-scale dimensions here would produce a nonsensical result.
Forgetting to subtract door and window openings from the wall area first, this calculator computes blocks for the full area entered, ignoring openings will overstate the true material need.
Both count discrete masonry units for a wall, but concrete blocks (CMU) are much larger than standard bricks and use nominal sizing that already accounts for the mortar joint, while the Brick Calculator asks for the brick's raw size and joint thickness separately.
Nominal dimensions describe a block's size including its allowance for a standard mortar joint, which is why a 'nominal 16x8' block is actually manufactured slightly smaller (commonly 15.625 in × 7.625 in), so that once mortared in place, it occupies the full nominal footprint.
No, this calculates blocks for the total wall area you enter. Subtract the area of any door or window openings from your wall area before entering it for a more accurate count.
Google AdSense Banner
This area will contain advertisements after approval.