/24 Subnet Mask ReferenceIPv4
The workhorse of the Internet: a /24 is 256 addresses with mask <code>255.255.255.0</code>, small enough to manage and large enough for most LANs. When someone says 'a Class C' or 'one subnet', odds are they picture a /24.
/24 facts at a glance
- Subnet mask
- 255.255.255.0
- Wildcard mask
- 0.0.0.255
- Binary mask
- 11111111.11111111.11111111.00000000
- Total addresses
- 256
- Usable hosts
- 254 (excludes network & broadcast)
- Block size
- 256 addresses (28)
- Typical role
- Standard LAN subnet
Example /24 networks
Three consecutive /24 blocks, starting at the /24 boundary that contains 198.51.100.0:
| Network | Usable range | Usable hosts |
|---|---|---|
| 198.51.100.0/24 | 198.51.100.1 – 198.51.100.254 | 254 |
| 198.51.101.0/24 | 198.51.101.1 – 198.51.101.254 | 254 |
| 198.51.102.0/24 | 198.51.102.1 – 198.51.102.254 | 254 |
How to calculate a /24 mask
A /24 mask sets the first 24 bits of a 32-bit number to 1 and leaves the remaining 8 bits as 0. In binary that reads 11111111.11111111.11111111.00000000, which converts to dotted decimal 255.255.255.0. Each block covers a contiguous run of 28 = 256 addresses, and every block starts at a multiple of that size. The wildcard simply flips every bit, giving 0.0.0.255.
Where /24 is used
- Standard office and home LANs, including Wi-Fi segments such as the ubiquitous <code>192.168.1.0/24</code>.
- Per-VLAN addressing in enterprise designs, one /24 per department or floor.
- The smallest prefix generally accepted across the global routing table; announcements longer than /24 are routinely filtered.
- Reverse DNS delegation happens on this boundary, as an x.y.z.in-addr.arpa zone maps to exactly one /24.
Why only 254 usable hosts: the lowest address identifies the network itself and the highest is reserved for broadcast, leaving 254 for real devices.
All three RFC 5737 documentation ranges are /24s: 192.0.2.0/24, 198.51.100.0/24, and 203.0.113.0/24.
One /24 splits into two /25s, four /26s, eight /27s, sixteen /28s, or sixty-four /30s.
Frequently asked questions
How many usable hosts are in a /24?
Exactly 254. The block holds 256 addresses, minus the network address at the bottom and the broadcast address at the top.
What is the subnet mask for a /24?
<code>255.255.255.0</code>, with wildcard <code>0.0.0.255</code>. Twenty-four fixed bits leave the entire last octet for host numbering.
Why does a /24 have 254 hosts instead of 256?
Two addresses carry structural roles rather than device roles: the all-zero host byte names the network and the all-ones host byte broadcasts to everyone on it.
How many /24s are in a /16?
256. Each occupies one value of the third octet, which is why /16-to-/24 planning feels so natural.
Is /24 the smallest routable subnet on the Internet?
In practice, yes: operators worldwide filter prefixes longer than /24, so anything smaller stays behind NAT or within a provider's network.
Open this block in a calculator
Open the /24 block in the subnet calculator