Subnet Calculator
Network, broadcast, host range and subnets for IPv4 and IPv6.
How to use the subnet calculator
Enter an address in any of these forms and press Calculate:
- CIDR:
192.168.1.10/24 - Address and mask:
10.0.0.1 255.255.0.0 - IPv6 prefix:
2001:db8:abcd::/48
An address without a prefix is treated as a single host (/32) for IPv4 and as a /64 network for IPv6. Everything is calculated in your browser.
What the results mean
| Field | Meaning |
|---|---|
| Network | The first address of the block, which identifies the network |
| Subnet mask | The prefix written as an address, like 255.255.255.0 |
| Wildcard mask | The inverse of the mask, used in router access lists |
| Broadcast | The last address, used to reach every device on the network |
| First / last usable host | The range you can assign to devices |
| Total addresses / usable hosts | Usable is two less than total, except for /31 and /32 |
| Reverse DNS zone | Where PTR records for this network live |
For IPv6 the calculator also shows the expanded address, the first and last address and how many /64 networks fit inside the prefix.
Splitting a network
Choose a larger prefix under Subnets to divide the network. For example, a /24 splits into four /26 networks of 64 addresses each. The first 64 subnets are listed.
Quick reference
| Prefix | Mask | Hosts |
|---|---|---|
| /30 | 255.255.255.252 | 2 |
| /29 | 255.255.255.248 | 6 |
| /28 | 255.255.255.240 | 14 |
| /27 | 255.255.255.224 | 30 |
| /26 | 255.255.255.192 | 62 |
| /25 | 255.255.255.128 | 126 |
| /24 | 255.255.255.0 | 254 |
| /23 | 255.255.254.0 | 510 |
| /22 | 255.255.252.0 | 1,022 |
| /16 | 255.255.0.0 | 65,534 |
See subnet masks and CIDR explained for the full table and how the math works.
Frequently asked questions
Why does a /31 have two usable hosts?
RFC 3021 allows /31 networks on point-to-point links, where no network or broadcast address is needed.
What prefix should a home network use?
/24 (255.255.255.0) is the default on almost every router and gives 254 addresses.
What IPv6 prefix should a LAN use?
Always /64. IPv6 address autoconfiguration expects it.
Learn more
What is IP allowlisting (whitelisting)?
IP allowlisting lets only approved IP addresses reach a server, admin panel or API. How it works, when it helps and its limits with dynamic IPs and VPNs.
Networking · 2 min readSubnet masks and CIDR notation explained
What a subnet mask like 255.255.255.0 means, how CIDR notation like /24 works, how many addresses each size holds, with a cheat sheet and examples.
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