Revenue passenger kilometres (RPK) is a measure of the volume of passengers carried by an airline.
The definition is:
Number of revenue-paying passengers x the distance traveled.
Note that only revenue-paying passengers are included in the calculation. Other non paying passengers - such as babies and very young children who do not have a seat of their own in addition to passengers traveling on freebies – are excluded.
By calculating the RPK for each plane in an airline’s fleet, the RPK of the fleet can be determined.