Subnet Calculator
IPv4 CIDR network, broadcast, mask, wildcard and usable host range — /31 and /32 included.
Calculate IPv4 Subnets and CIDR Ranges
Subnetting is bitwise arithmetic on a 32-bit number, and doing it in your head is entirely possible and entirely error-prone. A /26 gives 62 usable hosts, not 64, because the network and broadcast addresses are reserved — the kind of detail that produces an IP conflict weeks later.
This calculator takes an address with either a CIDR prefix or a dotted-decimal mask and returns everything: network, broadcast, first and last usable host, total and usable counts, wildcard mask and the binary breakdown.
Key features
- CIDR or dotted mask — enter
/24or255.255.255.0, whichever you have. - Complete range output — network, broadcast, first and last usable host addresses.
- Wildcard mask — the inverted mask that Cisco ACLs and OSPF require.
- Binary breakdown — the address and mask in binary, which is where subnetting finally makes sense.
- Class and scope noted — whether the range is private, loopback, link-local or public.
This tool runs entirely inside your browser using native Web APIs. Your files and text are never uploaded to a server, never logged and never shared with third parties.
How to use: Subnet Calculator
- Enter an IP address
Any address inside the subnet you are interested in — it need not be the network address. - Set the prefix or mask
A CIDR prefix from /0 to /32, or the equivalent dotted-decimal mask. - Read the results
Network, broadcast, usable range and host counts all appear together. - Check the binary
The bit-level view shows exactly where the network and host portions divide.
Technical specifications
| Processing location | Entirely in your browser — no server round trip |
|---|---|
| Data uploaded | None. Files and text never leave your device |
| Price | Free — no account, no trial, no usage cap |
| Category | Developer |
| Works offline | Yes, once the page has loaded |
| Browser support | Chrome 90+, Edge 90+, Firefox 90+, Safari 15+ |
| Interface languages | English, 中文, हिन्दी, Español, العربية |
Frequently asked questions
Why does a /24 have 254 usable hosts and not 256?
The first address in any subnet is the network identifier and the last is the broadcast address. Neither can be assigned to a host, so 256 total addresses give 254 usable.
What is a /31 for?
Point-to-point links. RFC 3021 allows both addresses in a /31 to be used because a two-node link has no need for a broadcast address. It saves two addresses per link, which adds up across a large network.
What is a wildcard mask?
The bitwise inverse of a subnet mask — /24 gives 0.0.0.255. Cisco access control lists and OSPF configuration use it instead of the subnet mask, and mixing the two up is a classic configuration error.
Which ranges are private?
10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 under RFC 1918, plus 169.254.0.0/16 for link-local and 127.0.0.0/8 for loopback. The tool flags these when your address falls in one.