If you use another set of units for margins, tabs and indents in your document, you can change the default measurement unit in writer. In the Tools menu select Options, expand the LibreOffice Writer section in the tree structure on the left and choose General. In the Measurement unit drop-down list choose your new unit. The ruler and any existing custom margin or indent settings will automatically convert to your chosen unit of measurement and display in the converted value. This setting applies to all documents open and future ones you create.
I am using English (Canada) as my language setting in my OS and the default measurement unit in writer is inches. I would like to change it to centimeters. How do I do this?