To a depth of 1 in 1 hour.
Gallons of water on roof.
Rainwater can be collected from the roofs using the rain water harvesting method.
This means that each square foot captures about 62 gallons per inch of rain.
For example on a 2 000 square foot roof you can collect 2 000 x 0 56 1 120 gallons inch of rain.
Take the dimensions of the footprint of your roof and convert them to inches.
1 of rain on 1 000 sf roof will yield 623 gallons.
Rainwater collection calculation formulas and equations.
To calculate the runoff from any given rainfall.
Rainwater collection calculator in gallons.
If your average rainfall was 25 inches year your annual collection potential is 1 120 x 25 28 000 gallons year.
Converting this to gallons per minute per square foot gpm ft 2.
So a 50 x 20 roof is 600 x 240 multiply the roof dimensions by the number of inches of rainfall.
In this example 600 x 240 x 1 144 000 cubic inches of water divide by 231 to get the number of gallons because 1 gallon 231 cubic inches.
The answer is about 623 gallons.
For every 1 inch of rain and 1 000 square feet of roof you capture about 620 gallons of water.
The collectable rainwater from the roof can be calculated in gallons using this calculator based on the rainfall and area.
Simply take your roof s square footage and multiply by 62.
How much will your roof be able to capture.
Roof area m2 x precipitation amount mm amount collected liters.
To find how much rain you can collect in an average rain year multiply this number by the average inches of rain.