I was planning on writing this great breakthrough piece on IPv6 subnet sizes, like how many /48s are in a /32 or how many /56s are in a /24, etc… But then I stumbled across a great PDF from ARIN and realized that all the work was already done. So I ended up not posting anything.
The ARIN Doc
I continue to get questions on this topic though, and the ARIN doc is actually a tad hard to find unless you already know exactly where to look for it, so I changed my mind and decided to just post up their chart here. It goes from /0 to /128 and compares classful, IPv4 and IPv6 subnets with the number of addresses in each prefix size for each address type listed. Then, on the last page, it also includes a list of IPv6 prefix lengths (subnet masks) and details the number of /48, /56 and /64 subnets within each one. All in all a great reference sheet to have handy when laying out IPv6 subnet plans. Take a look:
You can also find more great info from ARIN here. Enjoy!