making a rounded bag pattern

[Br4ndybuck]

I've finally decided to design my own handbag, but a little stuck on the pattern. It's a simple rectangular shape with rounded corners, and I want to add a zipper gusset to give it some depth.

I know the gusset length should be the perimeter of the bag, but I'm lost on how to get the measurement right with the rounded corners.
Just adding up the straight sides and lengths feels wrong. Is there a formula or a trick to account for the curve?
Any advice on how to calculate the gusset for those rounded corners would be a huge help!

 

[Wilhelm_Compass]

I've done this the lazy way... make a paper or cardboard mock-up of your bag front, then take a tape measure and walk it around the edge. That gives you the exact perimeter without overthinking formulas. Works better than math when your corners aren't perfect circles.

 

[cindystitches]

I think it'd be easier to make a quick paper or fabric mock up of your bag front, then run a measuring tape around the edge...the curves included and that should give you the gusset length without having to fuss with formulas

 

[ciarunji99]

I ran into the same thing when I made a round crossbody years ago. I agree with the replies above, I ended up tracing the full shape onto paper and used one of those soft measuring tapes to follow the edge. It gave me a way better sense of the gusset length than trying to do the math. Curious if you’ve tried that yet or if you’re working from a digital pattern?