# How to convert size represented in one prefix length to another?

Example, let's say if someone says, I have allocated one `/64` address. How can I convert that to a size in `/30`? How many `/30` equals to one `/64`?

How can I convert that to a size in /30?

This question does not actually make sense.

How many /30 equals to one /64?

Neither does this question make sense.

I assume you mean IPv6 because there is no such thing as an IPv4 `/64` network.

Your last question could make sense if you reverse it to ask how many `/64` networks can be made from a `/30` prefix. The way to calculate that is to subtract 30 from 64 to get 34. The answer would be 2 to the power of the result.

``````64 - 30 = 34
2^34 = 17,179,869,184
``````

That means you can derive 17,179,869,184 `/64` networks from one `/30` prefix.

For IPv6, you will probably divide your `/30` prefix into `/48` (or shorter) prefixes to assign each site a `/48` prefix. That means that you can have 262,144 sites, each with 65,536 standard IPv6 `/64` networks.

The reason to use `/48` (or shorter) for each site is that is the longest prefix that the ISPs will advertise on the public Internet.