Concrete Block Calculator — Blocks & Bricks for Walls
Wall Area (net)
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Blocks Needed (with waste)
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Blocks (without waste)
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Mortar Bags (80 lb) Estimated
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Estimated Block Cost
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Rows of Blocks
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Blocks per Row
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How This Calculator Works
This concrete block calculator helps you estimate the number of blocks or bricks needed for a wall or structure. Enter your wall dimensions, block size, and mortar joint thickness, and the calculator determines the total blocks required including a waste allowance. It also estimates mortar bags and optional cost.
The calculation divides the total wall area by the face area of a single block (including one mortar joint on the length and height). For example, an 8×16-inch block with 3/8-inch mortar has a nominal face area of 8.375 × 16.375 inches, or about 0.951 sq ft. The calculator then applies your waste percentage to the total count.
Accurate material estimation prevents costly construction delays and excess inventory. This calculator supports standard concrete blocks (CMUs), standard bricks, and custom block sizes. Whether you are building a retaining wall, foundation, garden wall, or house walls, getting the block count right before ordering saves time and money.
Frequently Asked Questions
How many concrete blocks do I need for a wall?
Calculate the wall area (length × height), subtract any openings (doors, windows). Divide by the face area of one block including mortar joint. A standard 8×16-inch block with 3/8-inch mortar covers about 1.125 sq ft of wall face. A 100 sq ft wall needs approximately 89 standard blocks. Add 5-10% for waste and breakage.
What is the standard size of a concrete block?
The most common concrete block (CMU) in the US is 8×8×16 inches nominal, which is actually 7-5/8 × 7-5/8 × 15-5/8 inches to allow for 3/8-inch mortar joints. Other common sizes include 4×8×16 (half block), 12×8×16 (for foundation walls), and 6×8×16. Standard bricks are 3-5/8 × 2-1/4 × 7-5/8 inches.
How much mortar do I need per block?
Approximately 3 standard bags (80 lb each) of mortar mix covers about 36 standard blocks. This equates to about 8.5 bags per 100 blocks. For bricks, you need roughly 6.5-7 bags per 100 bricks. Mortar consumption varies based on joint thickness, block size, and whether you fill cores. Always buy 10% extra.
Should I include waste in my block estimate?
Yes, always add a waste factor. For standard projects, add 5% for breakage, cutting, and damage. For complex walls with many corners, angles, or openings, add 10%. For first-time builders, consider adding 10-15%. It is better to have extra blocks than to halt construction for a shortage.