The /24 prefix: 256 addresses, 254 usable
A /24 is the most common subnet size on earth. It fixes the first 24 bits of an IPv4 address — three octets — and leaves the entire last octet for hosts, giving you a block of 256 addresses with the subnet mask 255.255.255.0. If your home network is 192.168.1.0/24, your devices all live in 192.168.1.x.
It was once called a "Class C" network, from the pre-1993 classful addressing era. CIDR replaced classes, but the /24 stuck around as the de facto small-network default because it maps neatly onto the octet boundary and onto how people read dotted-quad addresses.
| Prefix length | /24 |
| Subnet mask | 255.255.255.0 |
| Wildcard mask | 0.0.0.255 |
| Total addresses | 256 |
| Usable hosts | 254 |
The network and broadcast columns describe 10.0.0.0/24 as a concrete example — the mask, wildcard and host counts apply to every /24.
Why you lose two addresses
Of the 256 addresses in a /24, only 254 can be assigned to devices. The first address — host bits all zero, like 192.168.1.0 — is the network address: it names the subnet itself in routing tables and can't identify a host. The last address — host bits all one, like 192.168.1.255 — is the broadcast address: packets sent to it are delivered to every host on the subnet.
This network-plus-broadcast convention applies to every subnet size from /0 through /30. The two exceptions sit at the very end of the scale: a /31 point-to-point link (RFC 3021) has no broadcast and uses both addresses, and a /32 is a single host route with exactly one address.
Where /24s actually show up
Almost every consumer router defaults to a /24: 192.168.1.0/24, 192.168.0.0/24, or a vendor-specific variant. In offices, /24s are the classic one-subnet-per-VLAN size — big enough for a floor of desks, small enough to keep broadcast domains tight. Cloud VPC subnets are often carved as /24s out of a larger 10.x block for the same reason.
A /24 is also the smallest prefix you can announce on the public Internet. BGP filters almost universally drop anything more specific than a /24, so even if you only need 50 public addresses, a /24 is the minimum routable allocation.
Splitting a /24
Need two isolated networks instead of one? Split the /24 into two /25s of 128 addresses each — 192.168.1.0/25 covers .0–.127, and 192.168.1.128/25 covers .128–.255. Keep halving and you get four /26s, eight /27s, and so on. Each split costs you two more addresses to network-and-broadcast overhead, which is why subnetting smaller than you need gets wasteful fast.
CIDR Calculator
Run the math on 10.0.0.0/24 — or any other block
Frequently asked questions
How many IP addresses are in a /24?
256 total addresses (2^8, since 32 − 24 = 8 host bits). Of those, 254 are usable for hosts: the first address is the network address and the last is the broadcast address.
What is the subnet mask of a /24?
255.255.255.0. The first 24 bits are set to 1, which is three full octets — that's why /24 lines up so cleanly with the dotted-quad notation.
Is a /24 the same as a Class C network?
Effectively, yes. Class C was the pre-CIDR name for a 256-address block (192.0.0.0–223.255.255.0 range). CIDR made classes obsolete in 1993, but the /24 size inherited the role.
What's bigger than a /24 — a /23 or a /25?
A /23. The prefix number counts network bits, so a smaller number means fewer network bits and a bigger block: /23 is 512 addresses, /25 is 128. Every step down doubles the size, every step up halves it.