Examples
43.241.146.32/24
IPv6 documentation address /64
2001:db8:85a3::8a2e:370:7334/64 belongs to 2001:0db8:85a3:0000:: and contains 2⁶⁴ addresses.Formula
network = IP AND subnet mask
broadcast = network OR wildcard mask
IPv4 total addresses are 2^(32 − prefix). IPv6 total addresses are 2^(128 − prefix).
How to read an IPv4 subnet result
The CIDR prefix tells you how many of the 32 bits belong to the network. The
remaining bits identify addresses inside that network. For a /24, 24 bits are
fixed and 8 vary, so the block contains 2^8 = 256 addresses. The subnet mask is
255.255.255.0, and the wildcard mask is its bitwise inverse,
0.0.0.255.
For traditional multi-access IPv4 subnets, the first address identifies the
network and the last is the broadcast address. The calculator therefore reports
total − 2 conventional usable hosts. RFC 3021 permits special /31
point-to-point links, and a /32 identifies a single address; this page retains
the conventional zero-usable-host display for parity with its reference
calculator.
Common IPv4 block sizes
| Prefix | Subnet mask | Total addresses | Conventional usable hosts |
|---|---|---|---|
| /24 | 255.255.255.0 | 256 | 254 |
| /25 | 255.255.255.128 | 128 | 126 |
| /26 | 255.255.255.192 | 64 | 62 |
| /27 | 255.255.255.224 | 32 | 30 |
| /28 | 255.255.255.240 | 16 | 14 |
| /29 | 255.255.255.248 | 8 | 6 |
| /30 | 255.255.255.252 | 4 | 2 |
IPv6 prefixes are different
IPv6 addresses are 128 bits long. RFC 4291 writes a prefix as an IPv6 address
followed by a slash and prefix length. A /64 fixes the first 64 bits and leaves
64 interface bits, yielding 18,446,744,073,709,551,616 possible addresses.
IPv6 does not use an IPv4-style broadcast address, so the output focuses on the
network prefix, expanded address, address type, and block size.
Use the Scientific Notation Calculator to express very large IPv6 counts compactly, and the Conversion Calculator for ordinary measurement conversions.
Planning and validation notes
- Enter an address that belongs to the network; the calculator clears the host bits to derive the network boundary.
- Verify private, documentation, multicast, loopback, and other reserved ranges before assigning an address. A mathematically valid block is not automatically available for public use.
- Treat wildcard-mask syntax as platform-specific configuration guidance, not as a firewall rule ready to paste without review.
- Do not publish a real internal address plan merely to calculate its boundaries; the computation works just as well with a representative address.
Sources
Addressing scope
The IPv4 result shows network, broadcast, and conventional usable-host ranges; /31 point-to-point and /32 host routes have protocol-specific uses that differ from the classic host-count convention. IPv6 has no broadcast address, and a prefix calculation does not configure routing, neighbor discovery, firewalls, or address allocation. Refer to RFC 4632 and the IPv6 Addressing Architecture, RFC 4291 for the underlying conventions.
Network planning and access credentials
A subnet calculation plans addresses; it does not secure the router or the devices using them. If you also need a new account password, the Password Generator creates one on your device. Do not put passwords into the network address fields or include them in a shared calculation.