IPv4 / IPv6 Subnet Calculator
Switch between IPv4 and IPv6. Enter an address and a prefix length to get the network boundary, the host range, the address count, and the binary that shows exactly where the prefix ends.
Common prefixes
| Prefix | Netmask | Wildcard | Addresses | Usable hosts |
|---|
If you split this network further
| Prefix | Netmask | Subnets | Usable per subnet |
|---|
Reading a CIDR block
An IPv4 address is 32 bits and an IPv6 address is 128. The prefix length after the slash says how many leading bits identify the network; the rest identify the host. 192.168.1.10/24 fixes the first 24 bits, so the block covers 192.168.1.0 to 192.168.1.255.
In IPv4 the all-zero host part is the network address and the all-one part is broadcast, so a /24 has 256 addresses but 254 usable hosts. IPv6 has no broadcast address, so every address in the block is assignable.
Why IPv6 uses /64, /56 and /48
A /64 leaves 64 host bits, which is what Stateless Address Autoconfiguration (SLAAC) expects: devices build their own address from the prefix plus an interface identifier. Subnets shorter than /64 break SLAAC, which is why a /64 per LAN is the default even when you only need a handful of addresses.
In practice providers hand out a /56 or /48 and the site is carved into /64s: a /56 gives 256 subnets, a /48 gives 65,536. Those numbers are why IPv6 plans are usually drawn as a grid of /64s rather than as address arithmetic.
Point-to-point links are the exception: RFC 6164 recommends /127 so that neither end wastes a /64, and it avoids the neighbour-discovery problems of the older /126 habit.
Frequently asked questions
What does the /24 or /64 after an address mean?
The prefix length: how many leading bits identify the network. /24 fixes three IPv4 octets; /64 fixes the first four groups of an IPv6 address.
Why does IPv6 not have a broadcast address?
IPv6 replaced broadcast with multicast. Every address inside a subnet is assignable, so the usable count is the full 2^n rather than 2^n − 2.
How many addresses are in a /64?
2^64, about 18.4 quintillion. That is why nobody counts IPv6 addresses one by one — the calculator shows the exponent alongside the exact value.
Can I subnet IPv6 smaller than /64?
Technically yes, but SLAAC and most provider guidance assume /64. Use /127 for point-to-point links and /128 for a single host route.
Does this calculator handle IPv4-mapped IPv6 addresses?
Yes. Entries like ::ffff:192.168.1.1 are parsed and reported as IPv4-mapped, which is useful when reading dual-stack logs.