Enter the depth of rainfall from the storm and the duration of the storm into the calculator to determine the average rainfall intensity.

Average Rainfall Intensity Formula

The following equation is used to calculate the Average Rainfall Intensity.

ARI = RD / (T/60)
  • Where ARI is the average rainfall intensity (in/hr)
  • RD is the total rainfall that fell during the storm (in)
  • T is the total duration of the storm (min)

To calculate the average rainfall intensity, divide the total amount of rain by the duration of the storm.

What is Average Rainfall Intensity?


The average rainfall intensity is the amount of rainfall that a particular area receives in a given period. This can be measured in different ways and over different lengths of time.

For example, the average monthly rainfall intensity measures the total amount of rain that falls within one month.

The intensity of rainfall is the rate at which it is falling. The average rainfall intensity is the total volume of rainfall divided by the total duration of the rainstorm.

Rainfall can vary significantly in intensity, even within a relatively local area. A broad region may receive several inches of rain, but the heaviest rainfall may only be a few hundred yards wide because it was channeled by topography such as hills or mountains into a narrow band along the lee slopes.

Average rainfall intensities can be estimated from the size and duration of rainstorms within an area and from records of individual storms.

The former calibrates Doppler radar data and estimates rainfall patterns over large areas. Records of individual storms are used to calibrate rain gauges and determine the amount and duration of rainfall in extreme events such as floods.