1 of rain on 1 000 sf roof will yield 623 gallons.
Gallons of water on roof.
So a 50 x 20 roof is 600 x 240 multiply the roof dimensions by the number of inches of rainfall.
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.
For every 1 inch of rain and 1 000 square feet of roof you capture about 620 gallons of water.
Rainwater collection calculator in gallons.
Converting this to gallons per minute per square foot gpm ft 2.
Simply take your roof s square footage and multiply by 62.
Rainwater collection calculation formulas and equations.
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.
Roof area ft2 x precipitation amount in x 0 623 amount collected gallons easy formula to remember.
Roof area m2 x precipitation amount mm amount collected liters.
Rainwater can be collected from the roofs using the rain water harvesting method.
How much will your roof be able to capture.
The collectable rainwater from the roof can be calculated in gallons using this calculator based on the rainfall and area.
To calculate the runoff from any given rainfall.
1 inch of rainfall in an hour will cover 1 sq ft.
The answer is about 623 gallons.
If your average rainfall was 25 inches year your annual collection potential is 1 120 x 25 28 000 gallons year.
This means that each square foot captures about 62 gallons per inch of rain.