When planning a quilt- especially if you are designing your own- you want to keep in mind the finished size. Most pre-packaged batting comes in these standard sizes:
(some brands include an extra inch or so)
- King Size 124" x 120"
- Queen Size 90" x 108"
- Full Size 84" x 96"
- Twin Size 72" x 90"
- Baby Size 45" x 60"
- Craft Size 34" x 45"
Of course your quilt can be any size you like, but it's best to plan ahead so you have enough batting - ideally, a few inches larger than your quilt top.
you can purchase batting on the bolt. Most brands include widths based on these standard measurements, but you should check with your local quilt shop to see what is available.