Here's how I determine how much fabric is needed for my binding.
Take the length + width x 2. 68+93 = 161 x 2=322. Then divide that total by the width of your fabric. 322 divided. By 40 (on normal 42" fabric) = 8.05, which is how many strips of 40 inch fabric is needed for the 322 inch total length.
Now you need to determine how much fabric is needed, depending on the width of you binding. For 2 1/2 inch wide binding, take the 8.05 x 2.5 = 20.5 inches. I usually add another strip or two, just in case. So I would go for 24 inches or 2/3 of a yard.
Hope this helps for future binding needs.
This is almost how I calculate it - the differences are:
I add some inches for joins - I use a diagonal join - so that uses/wastes a bit more fabric
and
if I get a fraction for the number of strips needed, I round up to the next whole number.
68 + 68 + 93 + 93 + 24 = 346 (this is being conservative)
Divide that number by usable number of inches in width of fabric
we'll say that 40 inches is the usable width - you can check your width to make sure
346 / 40 = 8.65
You will need to cut
9 strips - there will be a little bit of left over strip when you are done
Multiply the number of strips times the width of binding you are using:
9 x 2.5 = 22.5 inches of
usable fabric length
Fabric is usually sold in 1/8 yard increments in the US - although some stores will sell fabric by the inch. Walmart and JoAnn are two places that do so.
5/8 yard = 22.5 inches
2/3 yard = 24 inches
I would buy at least 2/3 yard to allow for shrinkage - I am in the wash-before-cutting group - and/or to allow for wonkiness - or in case the cut is off - I would rather toss an inch than be short 1/4 of an inch.