Currency Converter
Fetching live exchange rate…
Label the Currencies and the Answer Stops Being Ambiguous
The hardest part of a currency conversion is not the multiplication — it is keeping track of which currency you started in and which one the answer is denominated in. A bare number like "1,180.00" tells you nothing on its own. This converter takes optional currency codes alongside the amount and the rate, and carries them through to the output, so the result reads as a quantity of a named currency rather than an unlabelled figure you have to annotate from memory.
The Formula
Underneath the labelling, the calculation is a single product:
The rate must be expressed in units of the to currency per one unit of the from currency. The calculator echoes the whole statement back — amount, from currency, rate, result, to currency — which makes a reversed rate obvious at a glance instead of silently producing a wrong answer.
Guard Rails
- A negative amount is rejected outright.
- A rate of zero or below is rejected — no currency has a non-positive price.
- Currency codes are optional. Leave them blank and the output falls back to the neutral labels "Currency A" and "Currency B".
- The product is rounded to six decimal places before being displayed to two.
Direction Is Everything
Suppose you hold 1,000 units of currency A and the quoted A-to-B rate is 1.18. Entering 1.18 gives 1,180.00 units of B. Entering the rate the wrong way round — using the B-to-A rate of roughly 0.847 instead — would return 847.00, an error of nearly 40%. The table shows how a fixed 1,000-unit amount responds across a band of rates.
| Rate (to per from) | You receive | Reciprocal rate |
|---|---|---|
| 0.80 | 800.00 | 1.25 |
| 0.90 | 900.00 | 1.111111 |
| 1.10 | 1,100.00 | 0.909091 |
| 1.25 | 1,250.00 | 0.80 |
| 1.60 | 1,600.00 | 0.625 |
Illustrative rates, not market quotes. The reciprocal column is simply 1 ÷ rate, and is the figure you would need to convert back the other way.
Situations This Handles Well
- Cross-border invoicing — converting an invoice total at the rate agreed in the contract, with both currency codes on the output for the accounting record.
- Expense claims — applying the rate that appeared on a card statement to each foreign-currency line item.
- Quoting a client abroad — working out what a price in your currency looks like in theirs before you send the proposal.
- Sanity-checking an app — confirming that a converted figure elsewhere used the rate and direction you assumed.
How to Use This Calculator
- Enter the From Currency code, such as USD. Optional, but it makes the output self-documenting.
- Enter the To Currency code, such as EUR.
- Enter the Amount held in the from currency.
- Enter the Exchange Rate as units of the to currency per one unit of the from currency, sourced at the moment of the conversion.
- Submit. Check the echoed statement reads the way you intended before using the figure.
Related Calculations
- Cross Currency Converter — when no direct rate exists and you must route through a third currency.
- Foreign Transaction Fee Calculator — add the card fee that the rate alone does not capture.