Unit Converter was downloaded and set up by over 5M users and its latest stable release was on Feb 18, 2019. In-app purchase items and ads can be found in this application. Samsung and LG users install the app quite often.
A free .apk file of Unit Converter 2.1.12 can be downloaded from Droid Informer and you can check out users' reviews on this site. Prepare 5 MB of free space on your device for this app installer and keep in mind that it runs on Android 4.2 and above.
Based on the users’ reviews, the strong side of the app is a great user interface.