/4 subnet.

What does /4 mean?

IPv4 addresses contain 32 bits. A /4 CIDR prefix means the first 4 bits identify the network and the remaining 28 bits identify addresses within that network. Because there are 28 host bits, the block contains 2²⁸, or 268,435,456, total IPv4 addresses. In practical terms, /4 is a very large address block typically encountered in routing or large allocations.

/4 subnet mask

The dotted-decimal subnet mask for /4 is 240.0.0.0. Its inverse wildcard mask is 15.255.255.255. These are different notations for the same network/host boundary: the subnet mask marks network bits with ones, while the wildcard mask flips those bits.

How many hosts are in a /4?

Under conventional IPv4 subnetting, a /4 has 268,435,454 usable host addresses after reserving the network and broadcast addresses.

How /4 boundaries behave

Because /4 spans more than 256 addresses, its boundary crosses one or more full IPv4 octets. Use the subnet calculator below with any host address to see the exact aligned network and broadcast addresses. Increasing the prefix to /5 halves the addresses in each child block. Decreasing it to /3 combines this address space with an adjacent block of the same size.

When would you use a /4?

The right prefix depends on route aggregation, host requirements, topology and operational policy rather than on a single universal rule. Large prefixes with smaller numbers represent broad address aggregates; prefixes closer to /32 represent progressively smaller blocks. For ordinary IPv4 LAN planning, always verify that the chosen prefix has enough conventional usable host addresses and leaves appropriate room for growth.

Compare nearby CIDR prefixes

Frequently asked questions

Use the interactive calculator below with a real IPv4 address, or open the complete subnetting cheat sheet to compare /4 with every other CIDR size.