Thread Length

I like to use one thread and two needles rather than two pieces of thread, this eliminates having to back-stitch when ya first start sewing.
To measure the length of thread we need just lay it along the sewing lines and add about another 4". Now double it. If we was using two threads this is the length you would need but since we are only using one you need to double it again. So the total length will be four times what your first measurement was.
I hope that's clear. I know how to make things but I am terrible at explaining it so others can understand. If it's not clear just leave a comment below and I will try and do a better job.