Best I found

I recently took a trip Down Under from the US I used this app before leaving and also while on trip to do all my conversions, at 1st I did not pay to use the update and honestly I dont think you need to. Now that Im back and want to return my cash to US I check it often to see when the best time to change my money back.
It did save me some cash especially if you are willing to take some time in converting

Flopper85 about Units Plus Converter