So I've been experimenting a little, with a round bag and rectangle w/ radius corners (1.75"radius), and have had a really difficult time getting the measurements to come out right. Does anyone have a good way to get it perty dern close on first go? These are felted wool with some 2/3oz veg tan, Palencia i think from Tandy. Overall I made it work, but had it bunch up at the last bit, and have had to unclip, and cut from the gusset usually. But it's easier that way than to add to it I think.
Here's the calculator i used for the rectangle https://rechneronline.de/pi/rounded-rectangle.php
And for the circle I used an excel calc that I found on utube.