A common question when attempting a masonry job is "how many blocks do I need?" This is required information if you do not wish to run short on blocks halfway through the job. And you certainly do not want to waste your money by buying far more blocks than you need. The good news is: the calculation for determining the quantity of concrete blocks is quick and painless.
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Things you need
- Tape measure
Measure the length and height of the wall to be blocked. If there is no structure present yet, you can acquire this information from blue prints.
Multiply the length and height to determine the wall's area. As an example, a 12 foot-by-20 foot wall would have an area of 240 square feet (sf).
Repeat this calculation if there are multiple walls to be blocked, and then add the figures. As an example, if you had area calculations of 240 sf, 480 sf, 480 sf and 240 sf, then the total wall area would be 1,440 sf.
Measure the length and height of any areas not requiring blocks, such as windows and doors. Multiply the length and height to acquire their areas and total the amounts. As an example, if you calculated area measurements for a 21 sf door and four 12 sf windows, then the total area of these excluded sections would be 69 sf.
Subtract the exclusions from the wall area. In the example, 1,440 minus 69 gives you 1,371 sf.
Multiply this square footage by 1.125 to calculate the number of concrete blocks required. In the example, this results in 1,542.375 blocks. Since you cannot purchase a fraction of a block, this is rounded up to 1,543 blocks.
This multiplier is based on standard 8 inch high and 16 inch long blocks. If you are using non-standard 8 inch-by-12 inch blocks, then use the multiplier 1.515.
Multiply the estimate by 1.10 to factor in breakage, splits and errors. In the example, your total number of blocks would be 1,698 blocks.
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