# How Much Rain Water Runs Off Your Roof?

You may be as astonished as we were to learn how much water runs off a roof in a rain storm!

Take a guess--what is the volume of water that runs off a 1,000 square foot roof during a 1" rain storm?

20 gallons? 50 gallons? 100 gallons? 1000 gallons?

The answer is about 623 gallons.

To calculate the runoff from any given rainfall:

Take the dimensions of the footprint of your roof and convert them to inches. (So, a 50' x 20' roof is 600" x 240".)

Multiply the roof dimensions by the number of inches of rainfall. (In this example, 600" x 240" x 1" = 144,000 cubic inches of water.)

Divide by 231 to get the number of gallons (because 1 gallon = 231 cubic inches). (144,000/231 = 623.38).