This information is taken from page 4 of “The Quilter’s Pocket Reference” by Peggy Scholley. (This is my favorite reference to have handy and contains much more valuable reference information.
Standard Bed - mattress - and Batting Sizes:
Crib – 27”x52” – 45”x60”
Twin – 39x75 – 72x90
Double/Full – 54x75 – 81x96
Queen – 60x80 – 90x108
King – 76x80 – 120x120
To get drop sizes, just add 20” to width for an additional 10” on each side and 10" in length for drop at bottom of bed, 24” width for 12 on each side and 12" to length for drop at bottom of bed, etc. Also, add 10 " to length to cover and tuck under pillow if you desire.