Have you ever wondered how much rain fell after a big storm? You may hear your meteorologist telling you that a few tenths of an inch, or an inch, fell through a given period of time. How much water in gallons does that mean for your yard or garden?

This is all about math and not so much meteorology.

To find out how much rain fell in gallons we will need to know certain variables to add to an equation.

The first variable is to find out how big of an area, in square feet, are you wanting to use to discover how much water fell. For example, we will use your backyard.

If your backyard is an acre, it is also 43,560 square feet. A half-acre would be 21,780 square feet.

The next thing you need to know is how much rain fell. Did a 1/2 inch fall? Was it an inch? It could have been 0.10″ of rainfall.

Once you know the area in square feet and the amount of rain, you can calculate the amount of water in gallons that fell in your area.

Here is how it works:
Take your square footage and then multiply it by the amount of rain in inches. You then take that number and multiply it by 0.623 and that will give you the number of gallons of water for the area you are using.

AREA(Square Feet) X RAINFALL(Number of Inches) X 0.623 = NUMBER OF GALLONS OF WATER ON AREA

Let’s look at some examples:

If your home is located on a half-acre acre lot, and the overnight storm dumped 0.50″ of rainfall at your location, what is the number of gallons produced by the rainfall?
A 1/2 acre lot is 21,780 square feet.
The math needed:
21,780 X 0.50 = 10,890
10,890 X 0.623 = 6,784.47
So, your half-acre lot created a total of 6,784.47 gallons of water from a 1/2-inch rainstorm!

If your home is located on a one-acre lot, and the overnight storm dumped 0.50″ of rainfall at your location, what is the number of gallons produced by the rainfall?
A one-acre lot is 43,560 square feet.
The math needed:
43,560 X 0.50 = 10,890
21,780 X 0.623 = 13,568.94
So, your one-acre lot created a total of 13,568.94 gallons of water from a 1/2-inch rainstorm!
That is almost enough water to fill up a swimming pool.

Let’s look at a township and see how much rainwater in gallons it can make with 0.50″ of rainfall.

We will use Boardman Township as our location. It could be any township, but we will use this as an example.

Boardman Township is 23.8 square miles. 23.8 square miles is equal to 663,505,920 square feet.
The math needed:
663,505,920 X 0.50 = 331,752,960
331,752,960 X 0.623 = 206,682,094.08
So, Boardman Township can create a total of 206,682,094.08 gallons of water from a 1/2-inch rainstorm!
That would make more than 25,000(8,000 gallon) semi-tanker loads of water! It would be more than 50,000 loads if an inch of rainfall fell.

Here is what you could expect from a 10-acre field, and the overnight storm dumped 0.50″ of rainfall at your location, what is the number of gallons produced by the rainfall?
A 10-acre lot is 435,600 square feet.
The math needed:
435,600 X 0.50 = 217,800
217,800 X 0.623 = 135,689.4
So, your 10-acre lot created a total of 135,689.4 gallons of water from a 1/2-inch rainstorm!
That would be around 17(8,000 gallon) semi-tanker loads of water.

You can see why a small amount of water can create flooding very quickly if the area is saturated, or the area is not drained very well with this volume of waterfall in a short period of time.