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)

FAQ

What factors can affect the accuracy of runoff volume calculations?

Several factors can affect the accuracy of runoff volume calculations, including the variability of rainfall intensity over the area, the slope and type of the terrain, the level of soil saturation before the rainfall, and the presence of vegetation or impermeable surfaces. These factors can influence the amount of water that actually becomes runoff versus what is absorbed into the ground or evaporated.

How can runoff volume calculations be used in urban planning?

Runoff volume calculations are crucial in urban planning for designing effective stormwater management systems. They help in determining the size of drainage systems, retention ponds, and other infrastructure needed to manage stormwater runoff. This is important to prevent flooding, reduce erosion, and protect water quality in urban areas.

Why is it important to measure runoff volume in gallons?

Measuring runoff volume in gallons (or other volume units) is important for practical applications, such as designing storage or treatment facilities for stormwater management. It allows for the quantification of water that needs to be managed, treated, or stored during and after rainfall events. This measurement is crucial for engineers, urban planners, and environmental scientists in making informed decisions to mitigate the impacts of runoff on both built and natural environments.