Currency
Currency conversion through a common base
Both currencies are expressed against the dollar, so the dollar cancels and only the ratio of the two rates survives.
The Formula
Target = amount x (target per USD / source per USD)
Both currencies are expressed against the dollar, so the dollar cancels and only the ratio of the two rates survives.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| A_s | Amount | currency | The amount in the source currency. |
| r_s | Source rate | rate | Units of the source currency per US dollar. |
| r_t | Target rate | rate | Units of the target currency per US dollar. |
What Each Symbol Means
A_scurrency
Amount
The amount in the source currency.
r_srate
Source rate
Units of the source currency per US dollar.
r_trate
Target rate
Units of the target currency per US dollar.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to convert currency page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Convert Currency, filed under Unit Conversion. Every number the guide produces comes from substituting into this one line.