Financial research concept

Passenger Revenue per Available Seat Mile (PRASM): Airline Unit Revenue

Passenger revenue per available seat mile measures passenger revenue generated for each unit of airline capacity. Learn how PRASM relates to yield, load factor, ASM, and total revenue per ASM.

By Lee BaileyPublished Sep 15, 2026
  1. Formula
  2. PRASM combines yield and load factor
  3. PRASM versus total revenue per ASM
  4. PRASM is not the same as passenger yield
  5. Worked example
  6. Why PRASM can be hard to compare across airlines
  7. PRASM and CASM
  8. What investors should check
  9. Real-world filing context
  10. Bottom line
  11. Part of the Airline Operating Model
  12. See It in Company Research
  13. Continue Research

Passenger revenue per available seat mile (PRASM) measures passenger revenue generated for each available seat mile of airline capacity.

It is one of the industry's most widely followed unit-revenue metrics because it combines pricing and capacity utilization in a single denominator-normalized measure.

Formula

PRASM = Passenger Revenue ÷ Available Seat Miles

If an airline earns $16 billion of passenger revenue on 100 billion ASMs, PRASM is 16 cents.

PRASM combines yield and load factor

A useful simplified relationship is:

PRASM ≈ Passenger Yield × Passenger Load Factor

Airline Passenger Yield captures passenger revenue per RPM, while Passenger Load Factor captures how much available capacity is filled by revenue traffic.

PRASM therefore can weaken because fares/yield fall, because load factor falls, or because both deteriorate.

PRASM versus total revenue per ASM

PRASM includes passenger revenue only. Total revenue per available seat mile, often called TRASM, uses total operating revenue.

That distinction matters for airlines with material loyalty, cargo, maintenance, credit-card, or other non-passenger revenue streams.

An airline can report stable PRASM while TRASM improves if non-passenger revenue grows faster than capacity.

PRASM is not the same as passenger yield

Yield uses RPM in the denominator. PRASM uses ASM.

If the airline discounts fares enough to fill more seats, yield may decline while load factor rises. The net effect on PRASM depends on the magnitude of each move.

That makes PRASM a useful bridge between pricing and utilization rather than a pure price metric.

Worked example

Suppose an airline reports:

  • passenger revenue: $17 billion;
  • ASM: 100 billion;
  • RPM: 85 billion.

PRASM is:

$17 billion ÷ 100 billion = 17 cents

Passenger yield is:

$17 billion ÷ 85 billion = 20 cents per RPM

Load factor is:

85 ÷ 100 = 85%

And the simplified bridge holds:

20 cents × 85% = 17 cents PRASM

Why PRASM can be hard to compare across airlines

PRASM is affected by network structure and accounting classification. Investors should consider:

  • domestic versus international mix;
  • premium versus main-cabin mix;
  • average stage length;
  • regional-carrier arrangements;
  • loyalty revenue classification;
  • ancillary revenue treatment; and
  • capacity growth timing.

Higher PRASM does not automatically mean a more profitable airline because cost structure can differ materially.

PRASM and CASM

PRASM is a revenue-side unit metric. Cost per Available Seat Mile is the cost-side counterpart.

The spread between unit revenue and unit cost can be directionally useful, but it is not a complete operating-margin formula when the revenue and cost numerators have different scopes or when adjusted CASM excludes fuel, special items, or other costs.

What investors should check

  1. Did PRASM move because yield, load factor, or both changed?
  2. How fast is ASM growing?
  3. How does PRASM compare with TRASM?
  4. Are premium and loyalty revenues changing mix?
  5. Is stage length affecting unit comparisons?
  6. Is the comparison reported or adjusted?
  7. Is CASM improving or worsening at the same time?

Real-world filing context

American Airlines defines PRASM as passenger revenue divided by ASM. United Airlines reports PRASM alongside yield, load factor, TRASM, and CASM, and Delta analyzes PRASM changes by geographic region with traffic and capacity changes.

Sources:

Bottom line

PRASM measures passenger revenue per unit of airline capacity. It combines pricing and utilization, so investors should decompose changes into yield, load factor, capacity, and mix rather than reading PRASM as a pure pricing signal.

Part of the Airline Operating Model

Connect capacity, traffic, load factor, passenger yield, unit revenue, and unit cost to understand airline economics.

How the model fits together
  • Capacity and demand: Passenger load factor equals RPM divided by ASM. RPM measures paid passenger traffic while ASM measures supplied seat capacity, so the ratio shows how much capacity is being absorbed.
  • Unit revenue and unit cost: When definitions align, PRASM equals passenger yield multiplied by load factor. CASM puts operating cost on the same ASM denominator, allowing unit revenue and unit cost to be read together without treating either as a complete profit measure.

See It in Company Research

These companies are examples of how the concept is reported or discussed in public filings. Definitions can differ by issuer; these links open company research rather than a normalized metric comparison.

Continue Research

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Compare passenger unit revenue

Compare airline PRASM while decomposing changes into passenger yield, load factor, capacity, and network mix.

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