As it is, the outlines of objects LOOK like halfway in and out of the object, but add to the OUTSIDE. For example: have a circle without outline, make it 10 mm x 10 mm. Add an outline of 1 mm. Look at circle's properties: it measures 11 mm x 11 mm. So the outline adds to the diameter of the circle. Now make this outline 5 mm. You'll see the diameter growing to 15 mm. BUT: the visual outline grows INTO the circle, making the inner plane looking smaller. Proof: make another circle 10x10 mm, no outline, 50% transparency, adjust the middles, see for yourself.

So it would be nice if this outline would also be visually added to the OUTSIDE.

Best of course would be to choose which way you want your outline: outside of object, inside, "halfway on border".

Thank you,
Salad

It's a known request: Facilitate outset/inset by half stroke width https://bugs.launchpad.net/inkscape/+bug/170898