What constitutes a "lot" of rain in terms of inches?

In the United States, generally, rainfall over 0.30 inches per hour is considered heavy.

1. Light rain: Generally up to 0.10 inches of rain per hour.
2. Moderate rain: Greater than 0.10 inches but less than 0.30 inches per hour.
3. Heavy rain: Greater than 0.30 inches per hour, or between 2.5 mm and 10mm per hour.
4. Very heavy rain: Greater than 2.0 inches per hour, or more than 50 mm per hour.

However, what is considered as "a lot of rain" also depends on the region and the time span over which the rain falls. For instance, an arid region experiencing 2 inches of rain in an hour would consider it a lot of rain as they are not used to heavy rainfall, but for a region accustomed to heavy rainfall it might not be considered as much.[3]

Learn more:

1. Precipitation: What Constitutes A Lot of Rain or Snow? - NOAA
2. Rain and Precipitation, USGS Water Science School
3. So You Know... How Much Rain Is Too Much Rain? - NWS