Instant subnet math as you type — network and broadcast addresses, usable ranges, masks, and host counts. The same engine that powers the Subnet Plus app, free on the web.
Edit any field — the others update instantly.
Browsers can't open raw network sockets — so live lookups and path tracing only run on-device. Subnet Plus brings the whole toolkit to your iPhone, iPad & Mac, and syncs your saved subnets over iCloud. Free to download.
Quick reference for prefix length, subnet mask, wildcard mask, and host counts.
| CIDR | Subnet mask | Wildcard mask | Total addresses | Usable hosts |
|---|---|---|---|---|
| /8 | 255.0.0.0 | 0.255.255.255 | 16,777,216 | 16,777,214 |
| /16 | 255.255.0.0 | 0.0.255.255 | 65,536 | 65,534 |
| /20 | 255.255.240.0 | 0.0.15.255 | 4,096 | 4,094 |
| /22 | 255.255.252.0 | 0.0.3.255 | 1,024 | 1,022 |
| /23 | 255.255.254.0 | 0.0.1.255 | 512 | 510 |
| /24 | 255.255.255.0 | 0.0.0.255 | 256 | 254 |
| /25 | 255.255.255.128 | 0.0.0.127 | 128 | 126 |
| /26 | 255.255.255.192 | 0.0.0.63 | 64 | 62 |
| /27 | 255.255.255.224 | 0.0.0.31 | 32 | 30 |
| /28 | 255.255.255.240 | 0.0.0.15 | 16 | 14 |
| /29 | 255.255.255.248 | 0.0.0.7 | 8 | 6 |
| /30 | 255.255.255.252 | 0.0.0.3 | 4 | 2 |
| /31 | 255.255.255.254 | 0.0.0.1 | 2 | 2 (RFC 3021) |
| /32 | 255.255.255.255 | 0.0.0.0 | 1 | 1 (host route) |
A subnet calculator takes an IP address and CIDR prefix such as 192.168.1.0/24 and works out the network address, broadcast address, usable host range, subnet mask, wildcard mask, and how many hosts the subnet holds. This one handles both IPv4 and IPv6 instantly in your browser.
A /24 has 256 addresses and 254 usable hosts; a /26 has 64 addresses and 62 usable hosts; a /30 has 4 addresses and 2 usable hosts. In general usable hosts = 2^(32 − prefix) − 2, except /31 (2 usable, RFC 3021) and /32 (a single host route).
A subnet mask such as 255.255.255.0 marks the network bits with 1s; a wildcard mask such as 0.0.0.255 is its inverse and marks the host bits with 1s. Wildcard masks are used in ACLs and OSPF. The Mask Converter tab converts between prefix, subnet mask, and wildcard.
Variable Length Subnet Masking (VLSM) splits one network into subnets of different sizes so each gets just enough addresses. The VLSM Designer allocates right-sized, correctly aligned blocks for a list of subnets and their host counts.
Yes. Enter any IPv6 address with a prefix, for example 2001:db8::/48, to see the network address, expanded and compressed forms, last address, total addresses, and address type.
Yes, it is completely free and works in any browser with no signup. For DNS lookup, ping, and traceroute, which need a real network device, download the free Subnet Plus app for iPhone, iPad, and Mac.
This free subnet calculator works entirely in your browser — nothing is sent to a server. Enter any IPv4 or IPv6 address with a CIDR prefix to instantly see the network address, broadcast address, usable host range, subnet mask, wildcard mask, total and usable host counts, IP class, and address type. It honors RFC 3021 (/31 point-to-point links) and /32 host routes, just like the app.
The web calculator covers subnet math: subnetting, VLSM planning, and mask conversion. The Subnet Plus app adds the tools that need a real device — DNS lookup, ping, and traceroute — plus iCloud sync, a saved library, history, and full offline use across iPhone, iPad, and Mac. It's been trusted by network engineers since 2013.