|The question of how many yards of thread a bobbin holds has come up over the years many times. I finally decided I wanted to know, once and for all.
Example...you've stay-stitched, understitched, topstitched, zigzagged, sewn most of a garment, and it's time to do the buttonholes. You don't want to run out of bobbin thread during buttonhole making. Is there enough left on that spool to fill another bobbin and still have enough left on the spool?
I searched online and found no answer.
I also realize there are variables...different machines use different sized bobbins...thread weight...and a balanced stitch [so you can assume you've used the same amount from the spool and the bobbin as you sewed].
My machine uses a very common bobbin that fits many different machines, so this test is based on that.
I used a brand new spool of thread from my stash, 40 weight, 100% polyester, 150 yards. I just kept filling bobbins until the spool was empty. It filled 2 1/2 bobbins. The "half bobbin" is, of course, a judgement call...it actually looked fuller than half, but the center of a bobbin is smaller than the outside.
So it turns out that a bobbin must hold approximately 60 yards of thread. By the time you've emptied a bobbin, you've used 120 yards from the spool. So if your spool originally had 240 yards or more, you can safely rewind another full bobbin.
For our metric members...60 yards is equal to 54.86 meters.