Free, no advertising and no need of permissions to install! You can move the slider to get a better measure. The "laser" that comes from the slider will tell you the exact length in centimeters. Just put the small thing on the screen, with one end at the 0cm position and move the slider to the other end.
This application was originally developed by Patán Libre and it is related to the Tools category. The most recent update of Ruler cm was launched on Sep 10, 2014 and the app was downloaded by over 100K users. On Google Play, this application was rated 3.2 by its users.
A lot of users set up the app on their Samsung and LG devices. Download the free .apk file of Ruler cm 2.1 and take a look at users' reviews on Droid Informer. The installer takes up 809 KB on disk and it runs on Android devices 2.2 and above. The antivirus report shows that the app is totally safe for usage.