How do I change scale to actual dimensions

I am new to sketchUp and am tracing a plan but can nt change its scale to match actual dimensions -help please

Where did you get the plan from and what format is it? The best way is to import a plan as .dwg or similar so you can scale it accurately inside SketchUp.

It is from my draftsman who was having trouble exporting the dwg file so it is in PDF format

Have your PDF/image laid flat at the origin [axes visibility on], in a new empty model.
Draw a temporary line over an edge in the image - which has a known length.
The longer that line the better.
Draw it as closely as you can too.
Use the Tapemeasure tool and pick the two ends of this line.
It will come up with a spurious value in the Measurements box.
Immediately type the known length of the edge - do NOT click on the Measurements box, simply type ‘in space’ and the value will appear in the Measurement box.
Press ‘enter’ and a dialog will ask you if you want to scale the whole model - answer ‘yes’.
Now the PDF/image and your temporary line are the expected size.
To double check, select the line and Entity Info should now show it correctly.
Delete that line unless you want it later…
I suggest you also use the context-menu to lock the PDF/image in place, so that any later overdrawing is not ruined if you accidentally move the base below !
You can lock PDF/images by making a group of them with a temporary line, and then editing that group and erasing the line. Groups and Component-instances can be locked in place - unlike ‘raw’ Images etc.


Thanks for your quick detailed response - i shall try that