What does inches of rain mean?

Answer 1

When rain falls it is usually fairly uniform over an area, so you can measure the amount of rain by saying that if all the rain in one day or other time period was contained in a tank with low sides and did not leak away into the soil, the height of the water surface in the tank would be a measure of the amount of rain falling on the area of the tank, in that time period. This is measured in inches, because for normal rainfall, excepting tropical storms, it is up to a few inches per day. Obviously the total amount of rain falling from a particular weather pattern occupying an area of square miles is impossible to measure, but at any point on the earth's surface you can easily measure the inches of rain by collecting it over a known surface area and channelling this rain into a measuring jar of some sort.

Answer 2

25.4mm