Rainfall Intensity
Calculator
Results
- Rainfall intensity (mm/h)
- 6
- Rainfall intensity (mm/min)
- 0.1
- Intensity class (1 light to 4 violent)
- 2
Weather results
| Rainfall intensity (mm/h) | 6 |
| Rainfall intensity (mm/min) | 0.1 |
| Intensity class (1 light to 4 violent) | 2 |
formula-map diagram
- Rainfall intensity (mm/h)
- 6
- Rainfall intensity (mm/min)
- 0.1
- Intensity class (1 light to 4 violent)
- 2
Weather relationship
Formula
I = rainfall depth ÷ duration; WMO bands 1 light (<2.5), 2 moderate, 3 heavy, 4 violent (mm/h)= 6
Note
This is a simplified model: it applies the published standard formula to the numbers you entered and ignores local terrain, radiation, precipitation type and instrument error. Wind chill is the 2001 NWS/Environment Canada regression, valid at or below 10 °C with wind at or above 4.8 km/h; the heat index is the Rothfusz regression, reliable above about 27 °C; dew point uses the Magnus approximation (a = 17.27, b = 237.7 °C) over liquid water; wet bulb uses Stull's approximation at standard sea-level pressure; pressure and density altitude assume the International Standard Atmosphere and dry air. Do not use these results for aviation, structural or safety decisions without an official forecast or a qualified professional.
More in Weather and climate
See all →Frequently asked questions
What's the difference between rainfall total and rainfall intensity?+
Rainfall total is the accumulated depth of rain over an entire event or period, while intensity is the rate at which that rain falls, typically expressed as millimetres or inches per hour, which describes how hard it's raining at a given moment rather than how much has fallen overall.
How is rainfall intensity calculated from measured data?+
It's the rainfall depth recorded over a short time interval, divided by that interval's duration in hours. Ten millimetres of rain in 30 minutes, for example, is a rainfall intensity of 20 mm/hour even though the total accumulation over the full hour might be different.
Why does the same total rainfall produce very different flooding outcomes?+
50 mm of rain spread evenly over 24 hours (low intensity) drains and infiltrates gradually with little flooding risk, while the same 50 mm falling in 30 minutes (very high intensity) can overwhelm drainage systems and cause flash flooding, even though the total volume is identical.
How is rainfall intensity classified (light, moderate, heavy)?+
Meteorological services generally classify roughly under 2.5 mm/hour as light rain, 2.5 to 7.5 mm/hour as moderate rain, and above 7.5-10 mm/hour as heavy rain, though exact thresholds vary slightly between different national weather agencies.
Why does rainfall intensity matter more than total rainfall for engineering design?+
Stormwater drains, culverts, and detention basins are sized to handle a peak intensity over a short design storm duration, not the total seasonal or annual rainfall, since the infrastructure needs to survive the worst short burst it's likely to see, not just move the average total volume over time.