Enter the total runoff area (ft^2) and the total inches of rainfall (in) into the Runoff Volume Calculator. The calculator will evaluate and display the Runoff Volume. 

Runoff Volume Formula

The following formula is used to calculate the Runoff Volume. 

RV = RA * RF/12 / 7.481

  • Where RV is the Runoff Volume (gallons)
  • RA is the total runoff area (ft^2) 
  • RF is the total inches of rainfall (in) 

How to Calculate Runoff Volume?

The following example problems outline how to calculate Runoff Volume.

Example Problem #1:

  1. First, determine the total runoff area (ft^2). 
    1. The total runoff area (ft^2) is given as: 50.
  2. Next, determine the total inches of rainfall (in). 
    1. The total inches of rainfall (in) is provided as: 2.
  3. Finally, calculate the Runoff Volume using the equation above: 

RV = RA * RF/12 / 7.481

The values given above are inserted into the equation below:

RV = 50 * 2/12 / 7.481 = 1.113 (gallons)


Example Problem #2: 

The variables needed for this problem are provided below:

total runoff area (ft^2) = 60

total inches of rainfall (in) = 3

Entering these values and solving gives:

RV = RA * RF/12 / 7.481 = 2.01 (gallons)