When I first started making bracelets this weekend, just about every cobra weave tutorial I found said "basic rule of thumb is 1'-0" of cord per 1" of bracelet". I made all of one bracelet using this method, a seven incher, and used all of five feet, even though I should have used seven. Two feet of waste is no good!
Break out the calculator:
5' divided by 7" (5/7=.71)
This is a good starting point. I so want a little bit of waste so I can at least finish my piece, so I went ahead and rounded up to .75. That's your factor.
So when you need to make, for example, an 8" bracelet, multiply:
That gives you 6'-0" of cord.
Using this factor, I've made a handful of bracelets since, and only end up with two small pieces of waste, averaging 2" in length, for each bracelet.