Revenue passenger miles (RPMs) and revenue passenger kilometers (RPKs) are measures of traffic for an airline flight, bus, or train calculated by multiplying the number of revenue-paying passengers aboard the vehicle by the distance traveled. On long-distance buses and trains (and some planes) passengers may board and disembark at intermediate stops, in which case RPMs/RPKs have to be calculated for each segment if a careful total is needed.
Revenue passenger miles can be considered the basic amount of "production" that an airline creates. The revenue passenger miles can be compared to the available seat miles over an airline's system to determine the overall passenger load factor. These measurements can further be used to measure unit revenues and unit costs.