If you’re only going to do one function, you might as well do it well. Oanda is a no-frills currency converter that does only that.
There’s a large selection of currencies available (we even found the Macau pataca! over 180 denominations are handy), but to prevent you from spending a large amount of time scrolling, the iPhone app remembers your list of most recently used currencies. A singular currency swap button also simplifies things.
What also makes Oanda a standout is that it can calculate typical interbank rates, standard ATM rates and typical credit card rates (transaction fee included) making it possibly more accurate in the long run. It is about as solid as Exchange Rates is for Android, which can notably compare multiple currencies against each other in one go.
However, the selection of rates and ease of use makes Oanda worth a try. Did I mention the app was also free? But if you need something a little bit more all-inclusive, try checking out our original post on conversion apps available out there.