There are many charts online that give you approximate sizes for quilts from crib to king size. They don't all give the exact same measurements, but are close. That should give you an idea.

Additionally , if you have a particular type of batting; sizes from the package or the on-line web site.
At times i dislike hacking from a roll. Other times i will patch pieces.

When making quilts for infants or toddlers I usually make them 5 x 7 or 6 x 8 rows depending on the size blocks I'm using.

I'm sure there is a standard size for beds and such but I measure whatever the quilt will go on and decide how much I want it to cover whether all the all to the floor if it's for a bed or just about a foot off the floor, etc. For lap quilts I want it to go all the way over my feet and up to my chest so that would depend on how tall you are. Then there are the specialty quilts going over chests, tables, etc. So I go by what I'm covering and not a standard size.

I like a square baby quilt but, if you want crib size, I believe it is usually 45 x 60". Beware the older quilt patterns--today's mattresses are thicker so need to allow for that extra drop that wasn't in those older patterns.

I found a long time ago that if I am using a 12" block I can go 5 blocks x 6 blocks with a 2" sashing to make the perfect full size quilt. If I want a larger quilt I add a row of 12" blocks x2 to make a queen and so on. So for a standard King you a 3 rows to 2 sides. At least this has always been my experience. The only one that is different it the California King. and I don't know the work around for that one. Of course don't forget the sashing. They always seem to have enough drop over the sides.