Depending on the project, I usually fill about 6 bobbins for a quilt. Each time I am sewing a longer piece of fabric (usually borders) I check to see if I am running low. I change the bobbin before I run out - I usually have no problems. When buying threads for a quilt with specific colors, I buy 2 spools of thread - 1 for bobbins and 1 to thread through my machine. Good luck!