Most generators are available in either long run or standard run tank size versions. A standard tank will last roughly 2 to 4 hours before needing to be refilled. A long run tank will be capable of running a generator overnight. If you are using your generator for short periods of time such as to power garden tools then a standard run tank should be sufficient. If you are using your generator is for emergency power back up then a long run tank is recommended.

Look at 'running time' or 'capacity' to compare tank sizes.