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.
I use an app called measures. Has any conversion i need.
The only two apps I see called measures are 4 and 6 years without updates.
This is the one i was talking about. I have used it routinely for years now. Weights, temps, measurements. It is my goto conversion app, but YMMV
Last version : 6y ago. ;-)