   SEARCH HOME Math Central Quandaries & 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.

Penny     Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences.