I'm doing it! ready to FMQ an oversize throw and don't know how many spools of thread to buy - I want to buy it all at the same time, for shipping $. I plan to use a stencil called "rose meandering" - the lines are about 1/2" apart. I'm pretty sure I want to use the same (king tut) thread in the bobbin. Only some of my possible colors come in a 2,000 yard cone; some come in only 500 yard spools. How much do I need?

Only your experience has the answer as stitch length and closeness determine how much you might need. I quilted a 48x60 size recently in shell pattern using walking foot and it took 5 bobbins. Second quilt same size and pattern took little over 3 bobbins as thread was thinner. So, I don't believe there is any formulae to determine how much you will need. Also, different machines take different amount on the bobbin. Your tension also effects it. Sorry but I don't believe there is any cut and dried answer. If you need to know for the future, then I believe you will have to buy more and then after finishing to keep a record of the amount used for the next time.

it really really depends on the size of the quilt, the density of the quilting, the thickness of your sandwich...if i were going to try it with the 500 yard spools i would get 5 or 6 of them just to make sure i had enough...with the cones i would think 2 would be plenty, one to use for bobbins, one for on top. once you do one you will have a much better idea on how much you use...you and i could both quilt the same quilt with the same thread and both use a different amount, so it is really hard for someone to tell you you will need 2500 yards, or whatever. it will also make a difference if you are new to quilting and find you have to take any stitching out...that's more thread...so, get more than you need at first. the left over thread can always be used for piecing later.

When I quilt a quilt I use a 1200 yard spool of thread. One is usually enough.

In general, lots. For a lap quilt with medium density stitching I usually fill 5-6 bobbins before starting. It will take almost 3 pre-filled ones.

I just did a 60x72 inch quilt with pretty dense quilting and used most of a 500 yard spool of Tut on just the top -- I used a different color for the bobbins and also for the border. So I would buy at least two for just the top alone.

But I try to buy thread either in very large quantities (colors I might use alot) or at the LQS so if I run out, I can always pick up another spool.