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SnapTools

CIDR / Subnet Calculator

Runs in your browser

Enter an IPv4 CIDR block to get its network address, broadcast address, netmask, and usable host range.

Network address192.168.1.0
Broadcast address192.168.1.255
Netmask255.255.255.0
Wildcard mask0.0.0.255
First usable host192.168.1.1
Last usable host192.168.1.254
Total addresses256
Usable hosts254

About this tool

CIDR notation (e.g. 192.168.1.0/24) packs an IP address and subnet size into one string, but reading off the actual usable range takes a bit of binary arithmetic — the network address, the broadcast address, and everything in between. This tool does that arithmetic directly, including the two special cases most calculators get wrong: /31 point-to-point links and /32 single hosts, where the usual "reserve the first and last address" rule doesn't apply.

How to use

  1. Enter a CIDR block, e.g. 10.0.0.0/24.
  2. If you enter a host address rather than the network address, it's normalised down automatically.
  3. Read off the network, broadcast, netmask, and usable host range.

When to use this tool

  • Planning subnet sizes before configuring a VPC, VLAN, or firewall rule.
  • Checking how many usable hosts a given prefix length actually provides.
  • Verifying a colleague's subnet plan doesn't overlap with an existing one.

Tips

  • /31 subnets (RFC 3021) are a special case for point-to-point links — both addresses are usable, with no network or broadcast address reserved.
  • /32 is a single host route — the network, broadcast and host address are all the same.

Limitations

  • IPv4 only — IPv6 prefixes are not supported.

FAQ

Does this support IPv6?
No — IPv4 only. IPv6 prefix arithmetic works differently enough that it deserves its own dedicated tool.
Is my input sent anywhere?
No. Every calculation runs in your browser.

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