*** Special Announcement *** I wrote an article on rain barrels for Fine Gardening magazine. It appears in the November / December 2008 Issue Number 124. In addition, they put together a very nice video showing how to build a rain barrel. While it varies a bit from our procedure, it's a good, helpful overview. |
Rainfall Collection Calculator
How can I figure out how much rainfall is needed to fill my barrels?
The easy way: A calculator
The harder way: Nitty-gritty details- 1 gallon = 231 cubic inches ≈ .1337 cubic feet
- 1 square foot = 144 square inches
- Surface area of the roof draining into barrels (Hint: you do not need to take into account the pitch, or slant, of your roof. You do have to take into account what fraction of your roof is emptying into rain barrels.For example, if you have a simple roof, say a rambler style house, and all the downspots in the back empty into rainbarrels, then the surface area emptying into rain barrels would be approximately 1/2 the width of your house times the length of your house. If you have two downspouts in the back and only one empties into a rain barrel, than it might be more like 1/4 the width times the length.)
(total capacity of barrels in gallons x 231)
---------------------------------------------------- = # of inches of rainfall to fill
(surface area in inches of roof draining into barrels)
Example:
- My house is about 60 feet long by 25 feet wide and half my roof empties into rain barrels, so the surface area in inches is 60 x 25 x 1/2 x 144 = 108,000 square inches
- I have 4 rain barrels at the backyard downspouts and they are 55 gallons each, so 4 x 55 = 220 gallons
So, (220 x 231) / (108,000) = 0.47 inches of rainfall needed
...that's less than a half inch of rain to fill my rain barrels with 220 gallons of water!
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