CASM
Acronym of cost per available seat-mile, a method of calculating operating costs in the travel industry, derived by dividing total operating expenses by total ASMs.
CASM: the airline's true operating cost per mile flown
CASM, cost per available seat-mile, is the metric airlines use to measure how much it costs them to operate each seat on an aircraft for one mile of flight. It strips away revenue figures entirely and focuses on the operational expense side. An airline calculates it by dividing total operating expenses (fuel, crew, maintenance, landing fees, catering, and all other direct costs) by the total number of available seat-miles (ASM) produced in the period. If an airline operates a 150-seat aircraft over 500 miles, that is 75,000 ASMs, regardless of how many seats were actually sold.
CASM is expressed in cents per mile. A typical full-service carrier in North America might operate at 10-15 cents per ASM, while ultra-low-cost carriers often operate below 8 cents. The figure varies enormously depending on stage length: short regional hops generate higher CASM because fixed costs like takeoff, landing, and crew layover time are spread across fewer miles. Long-haul international flights on large aircraft push CASM down because those same fixed costs are amortized across more seat-miles.
Why CASM matters for efficiency
CASM is not a profit metric, it is a cost structure indicator. Two airlines with identical CASM can have very different profitability if one fills its seats at 85 percent load factor and the other at 70 percent. But CASM reveals operational discipline. A declining CASM year-over-year often signals better fuel hedging, improved aircraft utilization, higher stage lengths, or renegotiated maintenance contracts. Rising CASM can point to aging fleets, unfavorable fuel prices, labor cost increases, or underutilized capacity.
The metric is most useful for comparing like with like: one full-service network carrier against another, or low-cost carriers within their segment. Comparing a regional carrier to an international long-haul operator using CASM alone is misleading because their cost structures are fundamentally different. Legacy carriers operating older, smaller aircraft on mixed route networks will have higher CASM than a new narrowbody operator flying high-density, long-range networks.
CASM excludes revenue and yield, which is both its strength and its limitation. It answers the question "how efficiently are we running the operation" but not "are we making money." Airlines also track unit revenues (revenue per ASM) separately to see the full picture. A carrier might improve CASM through cost cuts but lose profitability if those cuts harm product quality and yield.