I'm really anxious to try a Kaleidoscope quilt, and recall seeing a tut here on the Quilting Board which I'll have to locate again, but my question is, how do you know how much fabric to buy? I've read that there is very little waste, so I would guess that seams take up most of the "shrinkage" from the actual yardage purchased...?
Is there a rule of thumb for how much fabric to buy?
Thank you in advance for any help you can give.

Not so much the yardage, as the number of repeats below, or multiples of them.

OBW ... six repeats
4PP ... four repeats
OctagonKaleido ... eight repeats

Kaleidoscope quilt depends on how many sections in the block, you will need that many repeats in the fabric.
Google it.

There are a few differnt types of kaleidoscope quilt patterns, do mean the stack and whack or OBW types? With these type it will depend on the pattern repeat of the fabric. eg I have a fabric that I want to make a OBW out of, it has a pattern repeat of 24" and I need 6 repeats of the pattern, so I would need 4 yards (6 x 24") (I usually buy 5 so I have some of the original to put on the back). Hope this helps

Thanks Woody. I did not ask the origional question but was also wondering. Is there a formula or graph to show how much yardage needed for repeats/block size/bed size?

The six repeat look is what I would like to try ;)

Yes, this does help, at least I have a starting point. It's so fun to see the latest OBW's as they come on the board, and the amazing designs that come from some unlikley fabrics.