Hi ​@EmilyC1995 

Currently millimeter (mm) units or direct numeric input for wall dimensions in cm/mm is not achievable. Even if you change the document settings to cm, floor plan shapes often default to meters or feet.

To delegate, you can adjust the scale using the gear icon at the bottom left of the canvas and manually annotate dimensions. To learn more - How to set scale for a floorplan -- I'm missing something | Community

Hope this helps - Happy to help further!!
Thank you very much and have a great one!
Warm regards

Hi ​@EmilyC1995 

Thank you for your post.  Unfortunately,  as ​@Humas1985 has responded, the automatic floor plan measurement annotations are only available in ft or m (selectable via the setting gear as illustrated below), but Lucid is very interested in your feedback and is committed to continually improving our products. I have searched the Product Feedback section of the community, and I cannot find feedback specifically about measurement units, so could you please create raise a new product feedback idea outlining your use case.  This will allow other users with similar requests to discover your idea and improve upon it.
 

As an interim solution, can I suggest you set your units of measure to ‘m’ and then place a new box over the measurements, with your measurements in mm, and with a white background? This will cover the automatic measurements, and give readers the intended unit of mm (see example below)
 

Thank you, again for raising this

Craig