So I was trying to draw a board that would fit inside of an Altoids tin, and it turns out it’s phenomenally difficult to draw arcs. At least, if it’s not difficult, I’m totally doing it wrong. Even drawing a circle, I can’t specify a diameter. Seems like I should be able to do that for an arc as well. Instead, I get “Center X,Y and Point X,Y” I have no idea what those mean, so I was blindly playing with those numbers. Finally get one corner done so I copy it, then try to rotate it 90º to use in the next corner, and it goes wildly nuts. And suddenly those numbers I was playing with mean completely different things in the new orientation. Drove myself nuts for an hour coming up with 4 rounded corners for my board, and no two corners are the same. Is there a tutorial video about this sort of thing somewhere, or a how-to?
Try drawing arcs and circles graphically using the editor. Edit the numbers later if necessary. I just a drew a circle with a specific radius followed by four arcs with progressively larger radii at 90 degree increments around the circle and it took me about 20 seconds.
In the dialog boxes “Center” refers to the center of the circle or arc. “Point” is any point that lies on the circle. “Start Point” is the point on the arc where the arc starts and continues clockwise for the specified angle, which defaults to 90 degrees. “Item Thickness” is the width of the line used to draw the circle/arc.
You have some options here.
Draw it like @1.21Gigawatts suggested. (I would use a grid setting of no less than 0.5mm for this option. And stick to it for all outline features.)
Or use a CAD tool to get your parameters. I would use FreeCAD sketcher for that, just because i am familiar with it.
Here the workflow could be to draw your outline as a sketch and use reference measuremets to get the missing dimensions.
A simple example:
There was an issue with fabs failing with Gerber files with circles rather than a set of arcs
I am not sure about the etiquite of bringing an issue this.old back to life.
I am also working on a circular design and am kind of awestruck how clunky the tools are.
Maybe this is a separate issue but I’d like to see Kicad charge something for downloads and then pay programmers to fix some of the stuff that no one wants to work on.
Most times stuff 2 versions old isn’t very relevant. At least we didn’t have to read through dozens of posts this time. 
Please start a new thread.