255.255.255.0 Subnet Mask Explained (/24)
255.255.255.0 is the standard home subnet mask, or /24. Here is what it means and how many devices it allows.
255.255.255.0 is the subnet mask used by almost every home network. It means the first three numbers of an address identify the network and the last number identifies the device.
255.255.255.0 is the subnet mask used by almost every home network. The first three numbers of an address identify the network and the last number identifies the device, and in CIDR notation it is written /24, allowing 254 usable device addresses.
In CIDR notation it is written /24. It allows 254 usable device addresses.
255.255.255.0 at a glance
| Item | Value |
|---|---|
| CIDR | /24 |
| Network bits | 24 |
| Total addresses | 256 |
| Usable hosts | 254 |
| Example range | 192.168.1.1 to 192.168.1.254 |
| Broadcast | x.x.x.255 |
The 254-hosts row is the one I point at first when the mask looks cryptic.
How it works
In binary, 255 is eight ones. Three 255s mean 24 ones, which mark the network part. The final 0 leaves eight bits for devices, which gives 256 addresses minus the network and broadcast addresses.
Full explanation: what is a subnet mask.
The eight-ones picture is the one I use first when binary feels abstract.
When to use a different mask
- More than 254 devices: use 255.255.254.0 (/23) for 510 hosts.
- Small isolated segment: 255.255.255.128 (/25) gives 126 hosts.
- Always match: every device on the same network needs the same mask as the router.
The 510-hosts mask is the one I mention first when a home outgrows /24.
How to find the address you actually need
Most people who search for a special address are really looking for their router login or their own device address. Here is how to find both in under a minute:
- Router address (default gateway): on Windows run
ipconfigand read Default Gateway. On Mac open System Settings, Network, Details, TCP/IP and read Router. On phones open your WiFi network details. - Your device address: the IPv4 Address on Windows, IP Address on Mac and phones.
- Your public address: open our What Is My IP tool.
- Every device on your network: log in to the router and open the connected devices or DHCP client list.
Not sure which one is your router? Our Router IP Finder walks you through it step by step. The gateway-first check is the step I never skip when an address hunt starts.
Why almost every home uses 255.255.255.0
255.255.255.0 gives room for 254 devices, which is more than enough for nearly any home, even one packed with smart gadgets. It’s also the easiest mask to read: the first three numbers are the network and the last number is the device.
That simplicity is why router makers use it by default. Unless you’re running a large office or a lab, there’s no benefit to changing it. For me, the default mask is the one I leave alone in nearly every home.
Setting the mask on a static IP
When you give a device a manual address, enter the mask exactly as your router uses it:
- Windows and Mac: type 255.255.255.0 in the Subnet mask field.
- Android: enter 24 in Network prefix length, which means the same thing.
- iPhone: type 255.255.255.0 in Subnet Mask under Configure IP, Manual.
A wrong mask is a common cause of “connected but can’t reach anything” on devices with static IPs.
The wrong-mask failure is the one I warn about first with any static IP.
255.255.255.0 in binary
Computers see the mask as 32 ones and zeros: 11111111.11111111.11111111.00000000. The 24 ones mark the network part and the 8 zeros mark the device part. That’s why it’s also written as /24.
Eight zero bits give 256 combinations. Two are reserved (network and broadcast), leaving 254 usable addresses for devices. The 256-minus-two maths is the part I explain first when the count confuses.
Masks you might meet beyond home
- 255.255.255.128 (/25): 126 devices, half a /24.
- 255.255.254.0 (/23): 510 devices, two /24s joined.
- 255.255.252.0 (/22): 1,022 devices, common on campus networks.
- 255.255.255.248 (/29): 6 devices, often for small static IP blocks from ISPs.
The /29 block is the one I point at first when a small ISP block shows up.
Subnet mask vs IP address vs gateway
These three numbers always travel together in your network settings, and each does a different job:
- IP address (192.168.1.20): your device’s own address.
- Subnet mask (255.255.255.0): how big the local network is, so the device knows who’s a neighbour.
- Default gateway (192.168.1.1): where to send anything that isn’t a neighbour, which is your router.
If you ever type them in by hand, all three must agree: the IP and gateway must sit inside the same network the mask describes. The three-must-agree rule is the one I repeat most when numbers get typed by hand.
