How do I test the accuracy of a digital rain gauge?

To determine the accuracy of a digital rain gauge, you need to know the surface area of the funnel.

If the rain gauge has a rectangular inlet:

Area = length x width

If the rain gauge is circular:

Area = ( π x d2 ) / 4, where d is the diameter of the rain gauge.

The calculation is as follows:

Total Rain = Water Volume / Area


If the rain gauge is rectangular, and the surface area of the inlet is as follows:

Area = 11 x 5 cm or 55 cm2

If you pour in 100 ml of water (or 10 cm3 ) SLOWLY (over a 10 minute period), one would expect the rainfall to equal:

Total Rain = 10 cm3/ 55cm2 = 0.18 cm or 18 mm of rain (+/- the accuracy specification of the rain gauge).

Since 1 mm = 0.03937 inches, the total rain (inches) = 18 x 0.03937 inches/mm = 0.71 inches.

Take into account the resolution of the rain gauge.

If the resolution is 0.04 inches for example, the measurement would be 0.04 inches/tip x 17 tips = 0.68 inches.


1. My rain gauge is under reporting.
  • Make absolutly certain the rain gauge is level! If not perfectly level, the tipping mechanism will not work properly and under report rain.
  • Make certain there are no obstructions in the funnel and tipping mechanism. In heavy downpours, the rain droplets can "bounce" out of the rain gauge.
    There is an excellent discussion on rain gain modifications here: Rain Gauge Modifictions
2. My rain gauge is over reporting. Make certain the pole is not vibrating during windy conditions, causing false readings