Math CentralQuandaries & Queries


Question from Sean, a student:

Why do you use the number 144 to divide

EG. length of timber 2 inches x 8 inches x 14 foot = 1.5 cubic feet

Calculation is 2x8x14 =224 divide by 144 = 1.5 WHY 144 where does this figure come from

Hi Sean,

If you look carefully at the calculation you used to arrive at 224 (i.e. 2x8x14) you will see that two of these are measurements in inches and one of them is a measurement in feet. Usually calculations of this type are only done when all the measurements have been made using the same units.

The division by 144 is a conversion factor so that you get only one unit of measurement in your final result of 1.5 cubic feet. To see where it comes from, try performing the calculation after converting all of the measurements to feet instead of inches:

2 inches is 2/12 of a foot, 8 inches is 8/12 of a foot and the calculation becomes:

(2/12)(8/12)(14) = (2x8x14)/(12x12) = 224 divided by 144 = 1.5 cubic feet

Hope this helps,

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