How to convert currency manually
Multiply the amount by the exchange rate for one unit of the currency you have. If 1 US dollar buys 0.92 euros, then 50 dollars is 50 × 0.92 = 46 euros. To go back, divide: 46 ÷ 0.92 = 50 dollars.
The rest of this guide covers reading a quoted rate the right way round, a few shortcuts for doing it in your head, and working out what rate an exchange counter is really giving you. The rates below are examples, not today's rates.
Updated
Step by step
- Find the rate for one unit of the currency you have, for example 1 USD = 0.92 EUR.
- Multiply your amount by that rate: 120 × 0.92 = 110.40.
- If you only have the rate the other way round (1 EUR = 1.087 USD), divide instead: 120 ÷ 1.087 = 110.40.
- Round to the smallest coin of the target currency.
- Sanity-check the answer against a round rate you remember.
The currency conversion formula
Amount in B = amount in A × rate, where the rate is how much B one unit of A buys. The inverse rate is 1 ÷ rate: if 1 USD = 0.92 EUR, then 1 EUR = 1 ÷ 0.92 ≈ 1.087 USD.
A pair written as EUR/USD 1.0870 means 1 euro costs 1.0870 dollars. The first currency is the one you have one unit of. Mixing up the direction is the most common mistake, and it makes the answer wrong by roughly the rate squared.
Worked examples
| Convert | Rate | Sum | Answer |
|---|---|---|---|
| 120 USD to EUR | 1 USD = 0.92 EUR | 120 × 0.92 | 110.40 EUR |
| 4,500 JPY to USD | 1 USD = 150 JPY | 4,500 ÷ 150 | 30 USD |
| 80 GBP to EUR | 1 GBP = 1.17 EUR | 80 × 1.17 | 93.60 EUR |
| 350 MAD to USD | 1 USD = 10 MAD | 350 ÷ 10 | 35 USD |
Shortcuts for doing it in your head
- Round the rate first. 1 USD = 147 JPY becomes 150, so 4,500 yen is about 30 dollars.
- For big rates, drop zeros: at roughly 150 yen to the dollar, take 4,500, drop two zeros to get 45, then take two thirds: 30.
- For rates near 1, think in percent. If 1 EUR = 1.09 USD, add about 9% to a euro price to get dollars.
- Learn three anchors, such as 10, 50 and 100 in the local currency, and estimate everything else from them.
How to calculate the exchange rate you were given
Divide what you received by what you paid. Hand over 100 US dollars, get 88 euros back, and your rate was 88 ÷ 100 = 0.88 euros per dollar.
Compare that with a reference rate to see the margin. Against 0.92, you lost 0.04 euros per dollar, which is 0.04 ÷ 0.92 ≈ 4.3%. That's the number to compare between counters.
When to let an app do it
Mental math is fine for a coffee. For a long receipt, a tip, a split bill or crypto with many decimals, a currency calculator is quicker and doesn't round. Currency Offline does the sum and the conversion together, offline.
Questions
Do I multiply or divide to convert currency?
Multiply when the rate says how much of the target currency one unit of your currency buys. Divide when the rate is quoted the other way round. If the answer looks far too big or too small, you probably picked the wrong one.
How do I work out the margin an exchange office charges?
Divide what you received by what you paid to get their rate, then compare it with a reference rate. 88 ÷ 100 = 0.88 against a reference of 0.92 is a gap of about 4.3%.