An FX option premium is usually stated as units of the quoted currency per unit of underlying base currency.
Let us take the example of a USD/JPY option on an underlying amount of USD 10 million. The price in terms of the quoted currency is 2.11. This means that the option costs JPY 2.11 per dollar. Since the underlying is USD 10 million, the option price is JPY 21.1 million (2.11 x 10 million).