Currency Converter — live exchange rates for 60+ currencies

Foreign-exchange rates are quoted as the price of one currency in terms of another — for example, 1 USD = 302.5 LKR means one US dollar buys 302.5 Sri Lankan rupees on the inter-bank market. The rate you see on this page is the mid-market rate, defined as the midpoint between the bid (what a bank will pay you for the currency) and the ask (what it will charge you to buy it). Mid-market is the rate banks compare their margins against; it is not the rate retail customers actually transact at, but it is the right number to compare bank quotes to.

Every commercial rates provider publishes rates against a single base currency — usually USD. To convert from currency X to currency Y, the converter applies the standard cross-rate identity:

         amount × rateUSD→Y
result = ──────────────────
              rateUSD→X

where rateUSD→Ymeans “units of Y per 1 USD.” That single identity covers every pair in the catalogue — no special-cases for EUR or GBP, no different formula for currencies like JPY that quote with zero decimals. The math is exact in double-precision floating-point for any input under 10¹⁵, which is well above any practical amount.

Two safeguards run on every keystroke. First, the converter re-derives the answer via USD as an independent route (amount / rateX × rateY) and confirms it matches the cross-rate formula above. Second, the round-trip identity is checked: converting X→Y and then Y→X should return the original amount to within floating-point noise. If both checks pass, the “Round-trip verified” badge lights up in the calculator header.

Rates come from open.er-api.com, a free USD-base feed that aggregates the European Central Bank and several other central banks. The browser caches the table for one hour to avoid hammering the free endpoint. If the network is down, the converter falls back to an embedded reference table verified on 2026-05-11and clearly labels the badge as “Reference rates.”

• ExchangeRate-API — Free Open Access (open.er-api.com)
• Frankfurter — European Central Bank reference rates feed
• European Central Bank — Euro foreign exchange reference rates
• Central Bank of Sri Lanka — Daily Indicative Exchange Rates
• ISO 4217 — Currency codes (official register)

The cross-rate identity is universal — every commercial provider publishes USD-base rates and applies the same formula. The embedded fallback table was last cross-checked against the listed sources on 2026-05-11. The catalogue and decimal-places are reviewed annually against the ISO 4217 register.