Any crafter, woodworker or remodeler will probably need to subdivide a measurement at some point in a project. Equally dividing four feet into two parts may not require much thought, but equally dividing something like four feet and four inches into three parts may be slightly more difficult. A quick review of sixth-grade math, however, gives you all the necessary information. As long as you know that there are 12 inches in a foot, you can use basic multiplication and division to evenly subdivide any measurement.
Note the length of your measurement in feet and inches. For example, you may be measuring a board that is four feet, four inches long.
Convert your measurement into inches by multiplying the number of feet by 12 and adding the extra inches. In this case, multiply four by 12 to get 48, then add the extra four inches to get a total of 52.
Divide the number of inches by the number of subdivisions you want. If you want to divide your board into three equal parts, divide 52 inches by three, getting 17.33. This is the number of inches in each subdivision.
Divide the inches per subdivision by 12 to convert the measurement back into feet. The remainder represents the extra inches. In this case, divide 17.33 by 12 to get 1, with a remainder of 5.33.
Convert the decimal in the remainder into a fraction by placing it over 100 (or 1,000 if you have rounded to three decimal places) and reducing it. If you have a repeating decimal, such as .333, use a repeating decimal chart to find the equivalent fraction. In this case, .33 is equivalent to 1/3.
Add the fraction to the remainder from your division to find the exact number of inches to measure; in this case, measure each subdivision at 1 foot, 5 1/3 inches. To measure fractions of inches, multiply the fraction by 16 and measure to the resulting number of hash marks. In this example, (1/3) x 16 = 16/3 = 5 1/3, so measure to 5 1/3 hash marks beyond 1 foot, 5 inches for each subdivision.