SIMPLE RAINFALL CALCULATOR

It is not an uncommon misconception that the amount of water collected in a rain barrel is negligible, and how beneficial they can really be is often misunderstood. We have provided a very simple rainfall calculator to illustrate just how much free, clean water you could potentially collect from your home or outbuilding’s roof top.

Measure footprint of structure (home, garage, outbuilding, etc…)

Multiply length by width.
That will equal your total square footage.

In 1” rainfall event you will collect .6 gallons per square foot at 95% efficiency
(most common roof types).

Multiply your square footage by .6.
That will equal gallons collected in a 1” rainfall event.

Multiply gallons collected in 1” of rain by 39”.
That will equal water collected annually.

Count the number of downspouts on a building.

Divide the gallons collected in a 1” rainfall by the number of downspouts.
That will equal gallons per rain barrel.

EXAMPLE:

Building length (50) x building width (20) = square footage (1,000)

Square footage (1,000) x .6 = (600) gallons collected

(600) gallons x 39 (average annual rainfall in Cincinnati area) =
(23,400) gallons annually.

Number of downspouts on building (4)

(600) gallons ÷ (4) = up to 150 gallons per rain barrel

NOTE: This sample calculation demonstrates that you could fill a 50-gallon rain barrel with as little as 1/3 of an inch of rain and have a great source for watering gardens or filling watering cans for hanging baskets and planters. It is easy to see how much water could be potentially gathered and re-used with a collection system larger than a simple rain barrel. A rain barrel connected to your downspout—also known as a rainbank—is a great way to keep stormwater out of the system and to cut down your water bill! Because you are collecting right off the roof, it has few contaminants and is perfect for watering the garden.

Conserve energy AND do your part for the environment -- purchase a rain barrel at Marvin’s Organic Gardens today or call us at 513.932.3319 for an appointment to discuss rainwater collection ideas.