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 does its work inside your browser using native Web APIs. The files and text you give it are processed on your device and are not uploaded to our servers.
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.