This article summarises how you change the unit of measurement inside OnePlan.
Inside of OnePlan you have the option of using imperial or metric unit of measurement on your site plan. By default, OnePlan uses Imperial (US).
You can change the unit of measurement on a global basis for your event plan by clicking to access the menu in the top right. You will see your first name initials here too:
Then on the menu that drops down, use the switch to change to your desired measurement units:
This applies to the entire site plan. You're free to change it back at any time using the same method.