Math CentralQuandaries & Queries


Question from Matthew:

I need to calculate volume down to cubic feet. I pour concrete countertops and can't figure out the formula to convert inches and feet. If I have a 2.5 inch by 2 foot by 16 foot concrete countertop how do I convert it to cubic feet and hence know how many bags of concrete at .6 cubic feet per bag I will need. I am trying to input the formula into a spreadsheet. thank you so much Matt

Hi Matt,

The volume of a retcangular slab is the length times the width times the thickness, but all the dimensions need to be in the same units. You want a volume in cubic feet so you need all three dimensions to be in feet. There are 12 inches in a foot so 2.5 inches is 2.5/12 = 0.2083 feet. Thus the volume of your countertop is

16 × 2 × 0.2083 = 6.67 cubic feet.

An easier solution would be to just use our volume calculator.


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