The short answer
ROAS is dimensionless only when revenue and spend use compatible units. Dividing euros of revenue by US dollars of spend without conversion produces a number that is not a meaningful return ratio.
Choose a reporting currency and policy
Use the same currency for both sides of the calculation. Document the exchange-rate source, date, and conversion convention. A transaction-date conversion policy and a monthly average policy can produce different totals. Choose the method appropriate to the report and keep it consistent rather than switching to whichever result looks stronger.
ROAS = converted revenue ÷ spend in the same currency
Work through the conversion
Illustrative inputs: €4,000 of attributed revenue, $1,000 of ad spend, and an assumed rate of $1.10 per euro. This is a teaching assumption, not a live exchange-rate quote. Revenue converts to €4,000 × $1.10/€ = $4,400. ROAS is $4,400 ÷ $1,000 = 4.4×. Dividing 4,000 by 1,000 directly would incorrectly show 4×.
Separate currency movement from operating change
With the same €4,000 revenue and $1,000 spend, an alternative illustrative rate of $1.05 per euro gives $4,200 ÷ $1,000 = 4.2×. The difference between 4.4× and 4.2× comes entirely from the assumed conversion rate. It does not demonstrate that conversion rate, order count, or advertising efficiency changed in local currency.
Include costs on the same basis
When calculating a margin-based threshold, convert product, fulfillment, and other costs consistently too. A ROAS numerator in one currency and a break-even margin based on another unresolved currency mix can create a misleading comparison. Payment processing and currency-conversion fees are expenses, not merely an exchange-rate choice.
Reconcile platform and accounting views
Record the reporting currency of each export and check whether values were already converted before converting them again. For a management comparison, consider showing local-currency totals alongside the consolidated report. Keep actual settlements separate from analytical conversions when they differ. Without a known rate or conversion policy, report the currencies separately instead of asserting a precise combined ROAS.
Document the conversion policy
- Gather: Record source currency, reporting currency, rate direction, rate source and date.
- Produce: Convert compatible revenue and spend once, retaining the original amounts.
Decision boundary: A ratio change caused only by exchange rates is not evidence of better ad performance.
Next reading
Examples are illustrative, not client results or benchmarks. The calculations use the inputs shown; real-world decisions depend on your records and assumptions. Report a correction.