The default measurement unit in OpenOffice.org Calc can be changed using the Calc Options. To change the measurement unit, click Tools menu in OpenOffice.org Calc and select Options from the list of available menus.
In the options window, expand the OpenOffice.org Calc node available on the left hand side and select General Option. This would display the following the General Options window with option for changing the Measurement unit.
Click the Measurement unit dropdown and select the required value from the dropdown list. After selecting the value click OK to confirm and save the changes.