There are 231 cubic inches of water in a gallon so using our example above divide cubic inches by 231 and you have a total runoff of approximately 1870 gallons of water or 432 000 231 1870 129.
Gallons of water from roof.
In this example 600 x 240 x 1 144 000 cubic inches of water.
1 inch of rainfall in an hour will cover 1 sq ft.
Roof area ft2 x precipitation amount in x 0 623 amount collected gallons easy formula to remember.
Converting this to gallons per minute per square foot gpm ft 2.
Required roof drainage flow rate in gallons per minute 0 0104 x rainfall rate x roof area where rainfall rate is expressed in inches per hour and roof area is given in square feet.
To find how much rain you can collect in an average rain year multiply this number by the average inches of rain.
If your average rainfall was 25 inches year your annual collection potential is 1 120 x 25 28 000 gallons year.
To a depth of 1 in 1 hour.
Or maybe a low pressure cell has been napping overhead and your arm is hurting from holding that umbrella while you watch your basement fill up with water.
To calculate the runoff from any given rainfall.
Just a half inch of rain falling on a 1 000 square foot roof will yield 300 gallons of water.
The collectable rainwater from the roof can be calculated in gallons using this calculator based on the rainfall and area.
Rain barrel supplies list.
For sample purposes a 55 gallon barrel will be used.
1 of rain on 1 000 sf roof will yield 623 gallons roof area m2 x precipitation amount mm amount collected liters other water conservation calculators.
So a 50 x 20 roof is 600 x 240 multiply the roof dimensions by the number of inches of rainfall.
Convert the amount of rain from cubic inches into gallons.
When you look at the numbers it s surprising how much water you can collect every time it rains.
The answer is about 623 gallons.
Take the dimensions of the footprint of your roof and convert them to inches.
Give your rain barrel a thorough scrub at.
Rainwater can be collected from the roofs using the rain water harvesting method.
To get an idea how much water the roof of your own house might yield use the rainfall harvest calculator above.
Also outlined are the steps to build your own rain barrel to collect water from your roof and downspout for all outdoor uses like watering and cleaning.
Either way you would like to know how much rain has fallen how many gallons have come down from the skies onto your roof yard block or town.