| IP Address | |
|---|---|
| CIDR Notation | |
| Subnet Mask | |
| Wildcard Mask | |
| Network Address | |
| Broadcast Address | |
| First Usable Host | |
| Last Usable Host | |
| Total Addresses | |
| Usable Hosts | |
| Prefix Length |
Press Enter to calculate. Try 10.0.0.0/8, 172.16.5.9/20, or a /31 to see the RFC 3021 point-to-point exception.
When you’d reach for this
Subnetting questions show up in three places: cert exams (“how many hosts in a /27?”), address planning (“split this /24 across four VLANs”), and tickets (“is 10.20.3.9 in the same subnet as the gateway?”). The calculator answers all three, but do the math on paper first and let the tool referee. The Subnetting & CIDR lesson teaches the two-minute method.
| Prefix | Mask | Usable hosts | Typical use |
|---|---|---|---|
/24 |
255.255.255.0 |
254 | Office or home LAN |
/26 |
255.255.255.192 |
62 | A department or floor |
/27 |
255.255.255.224 |
30 | Small team or server group |
/30 |
255.255.255.252 |
2 | Router-to-router link |
/31 |
255.255.255.254 |
2 | Point-to-point (RFC 3021) |
Learn the math behind it
This tool pairs with Subnetting & CIDR (the worked examples use the same numbers), plus IPv4 addressing and NAT & private ranges.
Frequently asked questions
What does the /26 in an address mean?
The number after the slash is the CIDR prefix: how many leading bits of the 32-bit address identify the network. A /26 leaves 6 bits for hosts, so the subnet holds 64 addresses, 62 of them usable. It is the same information as the mask 255.255.255.192.
Why are only 62 of the 64 addresses usable?
Every classic subnet reserves its first address as the network identifier and its last as the broadcast address, so usable hosts are total minus two. The exceptions are /31 point-to-point links (RFC 3021) and /32 host routes, where both addresses are usable.
Does the calculator send my addresses anywhere?
No. The math runs entirely in your browser with JavaScript bit operations. There is no server call, no logging, and it works offline. Private addressing plans never leave the page.