Things You Will Need
Calculating the correct amount of insulation will prevent waste and needless return trips to the store for buying more insulation or returning overbought product. These calculations will determine the amount of cubic feet of blown-in insulation or the exact number of rolls of insulation that you will need to complete your job properly.
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Measure in inches the length and height of your walls. Multiply the length by the height.
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Measure in inches the height and width of any window and doors in the wall. Multiply the height by the width of all doors and windows individually. Add the results together.
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Subtract the results from Step 2 from the results you got from Step 1. This amount is the total amount of insulation you need in square inches. If you are blowing in the insulation, divide this number by 12. That will tell you how many cubic feet of insulation you need. If you are using rolls of insulation, go to Step 4.
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Measure, again in inches, the distance between your studs. Normally, this measurement is 16 inches. Divide the outcome of Step 3 by the approximate distance between your studs. This will result in the total number of inches of insulation in a roll of that width that you will need. Divide that number by 12 to see how many feet of insulation you will need for that width.
