MYOG Bivy

and it makes it a little easier to construct – if it’s rectangular

I don’t understand your question

(width + height) x 2 = circumference or girth

Sorry I wasn’t clear. English isn’t my first language ;)

As I understand it, to make the foot box I sew a diagonal sticht in both corners (just like a squared stuff sac). But I assume this will eat up some of the length and width of the fabric.

And how do I calculate how long that diaganol stitch has to be?

I hope this is a bit more clear.

ahhh….

English not first language consistent with using cm, I am hoping a day comes when the U.S. switches like the rest of the world : )

I do box bottoms like you’re saying.

In the picture of that bivy the bottom is a different material so it’s just a rectangular piece, no box bottom

If you want to do a box bottom:

Let’s say you want to make the bottom 60 cm wide and 45 cm tall

Make the fabric 22.5 cm longer.  I’m ignoring seam allowance, you have to add that.

First, sew the fabric together lengthwise to make a tube.  Then sew the end, flat.  The fabric was 210 cm wide, sewn flat it’s now 105 cm wide.

Mark two square shapes on each side:

You open up each corner and sew together the two sides of the box.

It’s a little non intuitive.  Maybe with this and you actually try it it will become understandable.

quick google search https://www.lazygirldesigns.com/tutorial-box-the-bottom-corners-of-a-bag/

I think it’s a cool topological construct

Jerry thanks! That makes it a lot clearer.

I was having trouble visualizing it. But I get it now… I hope ;)

If you mark those squares on both sides, then open it up, it becomes more obvious