How many miles is a 30 minute bike ride?

Can you elaborate on the distance a person might cover during a 30-minute bike ride? I'm curious to know how many miles on average someone would bike in such a timeframe, taking into account variables like terrain, fitness level, and cycling speed. Are there any standard estimates or general guidelines to help calculate this distance? Additionally, what factors would contribute to either increasing or decreasing the distance covered during a 30-minute bike ride?