@SuperSnekFriend @slashdot C-n <return>
e (ellipse tool)
Draw ellipse.
Set x y size in the menu to equal values to make a circle.
Image -> Guides -> New Guide (by Percent) -> 50% horizontal (optional)
Image -> Guides -> New Guide (by Percent) -> 50% vertical (optional)
e (ellipse tool) (optional)
Drag circle near the center and it snaps to the center (optional).
Select -> Border -> 2px <return>
Shift-b (Bucket fill tool)
Fill circle.
Now you have a perfect circle.


There is also another faster way to do it;
e (ellipse tool)
Draw circle.
Edit -> Stroke Selection -> Select stroke options -> <return>
Done.

I forgot about the latter way until now, as I've never wanted to draw a circle outline - I've wanted a filled in circle before and that's just ellipse tool + bucket fill tool.,