One (1.00) inch of rain A light moderate rain never reaches this amount, heavy rain for several hours (2-5 hours). There would be deep standing water for long periods of time.
How many inches of rain equals a gallon?
One gallon is 231 cubic inches, so an area of 231 square inches (roughly 23 inches x 10 inches) would hold one gallon of water if one inch of rain fell on it.