The currency conversion formula
Converted amount = starting amount × exchange rate. This formula assumes that the rate is quoted as destination currency per one unit of your starting currency.
For example, assume 1 EUR = 1.10 USD. To convert 50 EUR to dollars, calculate 50 × 1.10 = 55 USD. The units help you check the direction: euros multiplied by dollars per euro gives dollars.
All rates in this guide are invented for simple arithmetic. For a current estimate, use the currency converter and check when its data was updated.
When should you divide instead?
Divide when you are converting in the opposite direction of the quoted rate. If 1 EUR = 1.10 USD and you start with 55 USD, calculate 55 ÷ 1.10 = 50 EUR.
| Starting amount | Calculation | Result |
|---|---|---|
| 50 EUR | 50 × 1.10 | 55 USD |
| 55 USD | 55 ÷ 1.10 | 50 EUR |
Do not multiply in both directions by the same number. If you prefer always multiplying, calculate the reverse rate first.
How to find the reverse exchange rate
Reverse rate = 1 ÷ original rate. For the example quote, 1 ÷ 1.10 is approximately 0.90909. That means 1 USD is approximately 0.90909 EUR at the same underlying rate.
Multiplying 55 USD by 0.90909 gives approximately 50 EUR. Keep extra decimal places during the calculation and round the final amount, rather than repeatedly rounding each step.
Calculate a rate from two amounts
If you know a starting amount and the corresponding destination amount, divide the destination amount by the starting amount. For example, 110 USD ÷ 100 EUR = 1.10 USD per EUR.
When the amounts come from an actual exchange, check whether fees have already been deducted. A rate derived from the net amount received describes that particular outcome and may differ from a published reference quote.
Why might your bank show a different result?
A reference calculation and a transaction quote are not always the same. Providers may apply their own rates or fees, and the relevant rate may be determined at a different time.
The European Central Bank’s reference-rate page explicitly says its rates are published for information purposes and discourages using them for transactions. Use a converter to understand a value, then check the final quote from the service handling your exchange or payment.
Check your result in a converter
- Select the currency of the amount you already have.
- Enter that amount without a currency symbol.
- Select the currency you want to convert into.
- Check the direction, result, and freshness of the data.
For frequent comparisons, Worldwide Currency Converter on Android supports multiple currencies and cached offline rates. Learn how to compare several currencies, or prepare offline conversion before a trip.
Written by Lineium, publisher of Worldwide Currency Converter. App features: Google Play listing. Examples are illustrative unless explicitly stated otherwise.