How do I fit label precisely around bottle, specifically the circumference? I plan on wrapping a label around this bottle but the label gets distorted everytime, so I've concluded I need measurements to match. I've thought about making edge loops to get a specific height when making a selection and as for the circumference I can only think of counting all the faces and multiplying length times that. Am I on the right track? Let me know if there's a more effective way of achieving this.
To unwrap a cylinder in correct proportion:


Cut a vertical seam where you want it
Set an orthogonal view (poles or equator.. here, equator)
In edit mode, U unwrap  with 'Cylinder Projection' and settings as shown..





Oddly, in the 'Radius' field, entering pi*radius


.. which  doesn't make sense to me .. but there it is...