Bobbin Thread Estimator
Figure out roughly how many bobbins to wind before you start quilting or sewing a long project.
Where the capacity numbers come from
These are typical yardages for a standard-size (class 15) plastic bobbin, fully and evenly wound — actual capacity varies by machine, bobbin type (metal vs. plastic, standard vs. M-class or L-class), and how consistently the bobbin winder fills it. Treat these as a reasonable planning estimate, not an exact number for your specific machine.
Why heavier thread means fewer yards per bobbin
A bobbin holds a fixed volume of thread, and thicker thread takes up more of that volume per yard wound — so a heavier 40wt thread runs out sooner than a finer 60wt thread on the same bobbin.
Wind a couple of spares before starting a big project
Running out of bobbin thread mid-seam on a quilt means stopping, rewinding, and restarting exactly where you left off — annoying but manageable on a straight seam, much harder to hide on continuous free-motion quilting. Wind at least one extra bobbin beyond this estimate before starting anything you don't want to interrupt.