Scale drawing by specifying line width

For my part you are welcome, subplane.

It can be said that it is a matter of combining these two seemingly unrelated/contradictory  wishes/statements,

Your OP (original post) statement says,

"Is it possible to scale a whole drawing proportionally by specifying the width of one of the existing lines?"

and your latest posts says,

(I'm just trying to scale lengths and widths, stroke isn't important in this case)

And that combination, and the solution, is stated in the first post by Peter,

You can't scale it directly by specifying a width (or length) of one object, assuming the drawing has more than one. You would need to determine the percentage of increase or decrease that you want.

When you need to scale one or more objects by the total width or length, you can do it directly by inserting the desired W or H value in the Transform palette, and then press Ctrl/Cmd+Enter to keep proportions (unless they are locked together).

In all other cases, you will have do it indirectly with a calculation where you scale by the scaling percentage/factor which is the desired value divided by the current value.

Crucially, the indirect scaling can be determined/calculated for whichever value you can think of, including height or width of one object, or total height or width of any number of objects, or distance between two (sets of) objects,

or distance between any pair Anchor Point (which can be on the same or different objects), and crucially in your case the width of one of the existing lines = its Stroke Weight.

In all of these cases, the indirect scaling can be performed in the (Uniform box of the) Object menu > Transform > Scale that Peter pointed to.

Illy can perform one simple calculation for you in the form of multiplication/division/addition/subtraction involving two values, and no more is needed in this case because you know the two values that determine the scaling factor, namely the desired value and the current value.

Thank you so much for this solution! If only I remembered math class in grade school in the first place. I'm not quite following about Stroke Weight (I'm just trying to scale lengths and widths, stroke isn't important in this case), but that little formula did exactly the trick to figure out the percentage to scale everything at. Thanks again!

Indeed, Peter.

Maybe this is the first case ever where it is possible, and suitable, to say:

The long answer is yes and no.

Or no and yes.

This is becoming difficult.

You can't scale it directly by specifying a width (or length) of one object, assuming the drawing has more than one. You would need to determine the percentage of increase or decrease that you want.

You don't need to expand anything. If you want stroke weights to increase or decrease proportionally with the drawing, activate Scale Strokes and Effects in Preferences > General, the flyout menu in the Transform panel, or the More Options (…) section of the Properties panel (with at least one object selected).

Go to the Object menu > Transform > Scale, and enter the desired percentage into the Uniform field and click OK.

Peter

Hi yes you need to convert that to shapes first using expand or outline stroke....regards