LibreOffice Writer allows you to measure your margins, tabs, etc. in several different sets of units, such as inches, centimeters, and points. If you use something other than the default of inches it’s easy to change the unit of measurement in Writer.
To change the unit of measurement in LibreOffice Writer, go to Tools > Options.
In the tree structure on the left side of the Options dialog box, expand the LibreOffice Writer section by clicking the plus sign to the left of the “LibreOffice Writer” heading and then select “General”. Under Settings on the right, select an option, such as Centimeter, from the “Measurement unit” drop-down list.
Click “OK” to save the change and close the Options dialog box.
The ruler now measures in centimeters (or whichever unit of measure you selected). If you don’t see the ruler, it’s hidden, but you can show it.
The values of any tabs you already had on the ruler are adjusted to the newly selected unit so they remain in the same place on the ruler.
The unit of measurement change affects all documents that are open and ones you open or create after the change.