Round Corner Calculation

[jrprottas]

I'm making my first bag. The bottom piece is 4" deep x 9" wide. I'm using a single piece of leather for the front and both sides. the width of which would be (4+4+9), or 17". 

If I round the front corners of the bottom piece, what is the easiest and most accurate way to determine the new, shorter width of my front panel?

For instance, If I use a 1" diameter rounded  corner cut, is there a formula for adjusting the width of my front panel? Or do I use a cloth tape measure? Or is it just trial and error?

Thanks, Jeff

 

[blue duck]

The best way I have found is to do it on paper. Make a full size pattern and it will give you a very close idea. You will need to take into account the thickness of your leather and your seam allowances. Both of those things make it hard to give a specific formula. A cloth tape is going to get you close as well, but not exact. You could also take a strip of your leather and use it to measure. This is all if I have the design right in my head, do you have a sketch?

[fredk]

There is or are formulas to work it all out but I do it another way. I cut the shape and size of the gusset piece, less the allowance for the skived and folded join,  out of cardboard and use a fabric tape measure to measure round it. That gives me the front/base/back/across the top length for the inside of the leather that will be those sides. Then I just add how much I want the flap to come down over the front panel