Measure stablecoin swap cost in token units and market value

A stablecoin swap can be measured against one-for-one token parity and against relative market value. Keep both measures when they answer useful questions, but do not label them as the same execution cost.

Calculate both bases

Assume hypothetical input of 10,000 A, with A valued at $0.998 and B at $1.00. The quote returns 9,970 B before separately paid costs.

• Nominal-parity gap: 10,000 − 9,970 = 30 B, or 0.30% of nominal input units.
• Market-value benchmark: input value is $9,980, so quoted output is $10 below that benchmark, approximately 0.1002%.

The 30-unit parity gap includes a 20-unit initial relative-value difference plus a 10-unit quote shortfall. If separate gas is $2, add it to the economic ledger without changing the raw token-parity gap.

Neither benchmark is automatically executable

The market reference can itself come from a small trade or another venue. Label the resulting gap as relative to that reference, not necessarily avoidable cost. Stable-pool pricing still depends on the size and state of the requested conversion.

Parity is useful when the user's obligation is expressed in a fixed token count. Market value is useful when assessing economic value exchanged. They describe different constraints.

Report the assumptions explicitly

State the input and output assets, reference prices, timing and fee treatment. Do not silently force both tokens to $1 in a live analysis. If their relative price is uncertain, show token quantities and a sensitivity range rather than selecting the valuation that makes one route look favorable.

A price-reference revision can change the market-value shortfall without changing the received token count. Keeping the two bases separate makes that distinction visible and prevents nominal peg deviations from being attributed entirely to the execution provider.