When I was an Android user I found a fantastic free app call Convertbee and it converted pretty much any unit to any other unit you can imagine. It also did currency.

Since I switched to iOS full time I have not found a great replacement. I have been using Units Plus and went to pay for your full version, however it has not had an update in 2+ years and I worry about it being abandoned (looking at you Bean for Lemmy).

Looking for a replacement app available in the US. Thanks.

ETA: I have no issue paying for the app, but absolutely no subscriptions.