Do you mean how much of one is worth in another, or do you mean convert from one currency to another currency like an exchange house? 

 Yes, I want to see how much is one worth in another. 

 I don't know of a dedicated app.

The Cake wallet has conversion built into it's "Exchange" pane. 

 Xe.com/ucc install to home screen 

 Thx 

 They have mobile apps too