Originally Posted by
DogHouseMom
I am just not sure if to get a proper circle if the outside curve and inside curve are the same. I just need to work out the geometry.
Do you mean because of the seam allowances?
The sewing lines will have the same diameter, obviously, on both pieces of fabric (circle and background).
All the GREEN lines are the same length - 4 inches in this example.
(It doesn't look like it but they are.)
The black represents part of the fabric used for the seam allowances.
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Many of the circle rulers can cut either piece taking into account the SA.