How to Calculate Rainfall in Millimeters
- 1). Mount the rain gauge in an open area outside away from trees and other obstructions. Follow the manufacturer's printed instructions on the gauge.
- 2). Allow the rain gauge to collect water through the entirety of a storm or rainfall.
- 3). Note the level of the water inside the rain gauge after the rainfall has stopped. If the measurements are listed in centimeters rather than the desired millimeters, simply multiply the centimeter reading by 10. For example: 4 centimeters of rain in the gauge equals 40 millimeters of rain.
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