DEFINITION of 'Cost Per Available Seat Mile  CASM'
A common unit of measurement used to compare the efficiency of various airlines. It is obtained by dividing the operating costs of an airline by available seat miles (ASM). Generally, the lower the CASM, the more profitable and efficient the airline.
INVESTOPEDIA EXPLAINS 'Cost Per Available Seat Mile  CASM'
CASM is usually a more comprehensive measurement of airline costs, but it's still important that investors are aware of what items comprise this measurement. Many carriers exclude fuel costs from operating expenses, making the CASM an unreliable metric. Cost per available seat mile, as the name suggests, reflects the costs incurred by an airline to fly a single seat one mile.
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