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Rainfall, by the numbers

20 mm in 6 hours

An average rate of 3.333 mm per hour. Here’s what that amount means, in water and in motion.

Moderate · average intensity

The rain is illustrative. Actual intensity varies within a storm.

The quick answer

3.333 mm/hrAverage rainfall rate
Total water per m²
20 litres
Depth in inches
0.787 in
Across a 100 m² area
2,000 litres
Adjust in the explorer

Volumes assume no runoff, evaporation or infiltration.

Amount and intensity are different.

20 mm tells you the total rain. Dividing that amount by 6 hours gives the average hourly rate of 3.333 mm/hr.

This falls in the explorer’s “moderate” display category. Brief peaks could be higher, and weather services may use different category thresholds.

See how the scale works →

What happens on the ground?

Soil, slopes, drainage, earlier rain and the shape of the storm all matter. A rainfall total alone cannot tell you whether a place will flood or whether travel is safe.

For conditions where you are, check official local forecasts and warnings. Use this page to understand the quantities.

Weather data & references →

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