Creating a Rain Harvesting Plan

Owning a rain barrel will have many benefits for your home and wallet. There are many factors that go into determining your rain water harvest: how much your rain barrel can catch, how much you will need to use, and how easy it is to implement.

The amount of water your rain barrel will collect depend on the amount of rainfall, the location of the rain barrel, the size of your catchment area and the maximum capacity of your rain barrel.

  • The amount of rainfall cannot be controlled and varies across the US. To find your city's average rainfall click here.
  • Placing your rain barrel at the end of a downspout will allow for the most water to be collected.
  • The catchment area is based on the area of your roof (see calculator below).
  • You will choose how large of a barrel you will want.

How to calculate

Calculating how much rain you can collect is based on the area of your roof an easy length x width formula. Once the area is calculated you will use the following formula to determine your catchment area:

(L + gutters) x (W + gutters) = Catchment

It’s important to know that for every 1" of rainfall on a 1,000 square foot roof, there are 600 gallons of rain water that will be available. Now to calculate the amount of rain you will be able to capture, use the following formula:

A = (catchment area of building)   

R = (inches of rain)

G = (total amount of collected rainwater)

(A) x (R) x (600 gallons) / 1000 = (G)   

Calculate your water collection

Use our simple rain fall calculator to determine how much your roof will catch!

Enter your roofs area in square feet:


1" of rain fall = Enter roof area above

How much water is needed

Calculating your average outdoor water usage will hep you decide how large of a rain barrel you will need and how many. Here are some facts that may help you determine how much water you'll need to store:

  • The average family of 4 uses about 42 gallons of water a day for outdoor uses like watering the lawn (for just 20 minutes - 2 times a week), cleaning outdoor patio furniture, and washing cars. That’s 294 gallons a week!
  • The average lawn, depending on the climate, needs about 1 to 1.5" of water a week.
  • Washing the car can use between 150-180 gallons of water if the hose is left running (just 65 if you use a bucket to wash and rinse with the hose).
  • 30% of water used on the East Coast goes to watering lawns, 60% on the West Coast!

To determine how much water your lawn or garden requires calculate the area - another simple length x width equation. The multiply the area by .625 (equivalent to 5/8 gallons) to find the gallons of water used to apply 1" of water.

Your savings

By reusing rain water you will reduce your use of municipal or well water. This will save the local water supply and reduce your water bill by up to 50% in the summer months.

You can calculate the cost of watering your lawn to see how much you will save! Simply divide the number of gallons used by 1,000 then multiply by the price you pay per 1,000 gallons. For example, if in the area you live it costs $3.00 per 1,000 gallons of water that means that to water a lawn that is approximately 5,000 square feet the cost is about $9.50. If you water your entire yard once a week during the summer, the cost could add up to $40 or more each month. At that rate, your new rain barrel will pay for itself in just a few months!

Rain barrels are especially useful for saving rainwater for water shortage situations. Many states deal with droughts in the spring and summer months, and thousands of cities enforce water bans to conserve water during these times. By saving rainwater during the wetter seasons, you'll have plenty to use without letting your lawn or garden dry out during the summer. If you’re in an area that doesn’t experience frequent drought, just imagine how much money you could save by investing in a rain barrel and using much less public water!