Math CentralQuandaries & Queries


Question from marvin, a parent:

How many cement blocks do i need to build a 8 ft. tall wall x 1,300 ft. long?

Hi Marvin,

Standard concrete blocks are 15 5/8 inches by 7 5/8 inches and there is usually  3/8 inches of mortar between them so in the wall it is safe to say that a block and mortar on two sides is approximately 16 inches by 8 inches. Your wall is 1,300 feet long which is 1,300 × 12 = 15,600 inches long. Thus it will take 15,600/16 = 975 block to lay one course. The wall is 8 feet high which is 8 × 12 = 96 inches high. 96/8 = 12 so the wall will be 12 blocks high. Thus you will need 975 × 12 = 11,700 blocks.

This number may need to be modified somewhat depending on way the wall is constructed. In particular if you use a running bond you will need half blocks at the ends of every other row.

I hope this helps,

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