Set Measurement Scale same as background image?

[Ltek]

I have a floorplan diagram (JPG) I need to match the scale on and place items in correct locations, with correct scale, and add correct measurements tags.

How can I set the scale of draw.io to match the imported JPGs measurements?

Side note: I imported the floorplan JPG a layer since importing as a background Draw.io doesnt seem to properly scale the JPG onto a single 8.5x11 page -- which is what Draw.io is set to; even with the image being 4:3, the same scale.
Thx for the help!