A cross rate is a foreign currency exchange transaction between two currencies that are both valued against a third currency. In the foreign currency exchange markets, the U.S. dollar is the currency that is usually used to establish the values of the pair being exchanged.
Example - The cross rate should equal the ratio of the two corresponding pairs,
therefore, EUR/GBP = EUR/USD divided by GBP/USD,
just like GBP/CHF = GBP/USD x USD/CHF.
For example, suppose we know the bid and offer of AUD/USD and NZD/USD, and we want to profit from AUD/NZD.