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Subnet Calculator
A free IPv4 subnet calculator. Enter any IP address and a CIDR prefix between /0 and /32 and get the network address, broadcast address, subnet mask, wildcard mask, usable host range, and total address count: the same answers you would derive by hand on the CCNA exam.
Network
192.168.1.0/24
Broadcast
192.168.1.255
First usable host
192.168.1.1
Last usable host
192.168.1.254
Subnet mask
255.255.255.0
Wildcard mask
0.0.0.255
Total addresses
256
Usable hosts
254
How to use this calculator
- Type an IPv4 address into the IP field. Any host inside a subnet works; the calculator finds the network.
- Type a CIDR prefix length (0 to 32) or pick a preset.
- Read the network address, broadcast, and usable host range. Verify your manual calculation matches.
- For deeper coverage, read our subnetting guide for the manual fast method.
Common subnet sizes
| CIDR | Subnet mask | Total hosts | Usable hosts | Typical use |
|---|---|---|---|---|
| /24 | 255.255.255.0 | 256 | 254 | Home / small office LAN |
| /25 | 255.255.255.128 | 128 | 126 | Half a /24 |
| /26 | 255.255.255.192 | 64 | 62 | Department subnet |
| /27 | 255.255.255.224 | 32 | 30 | Small workgroup |
| /28 | 255.255.255.240 | 16 | 14 | Tiny segment |
| /29 | 255.255.255.248 | 8 | 6 | Server cluster |
| /30 | 255.255.255.252 | 4 | 2 | Point-to-point WAN link |
| /31 | 255.255.255.254 | 2 | 2 | P2P link (RFC 3021) |
| /32 | 255.255.255.255 | 1 | 1 | Single host (loopback) |
Subnet calculator FAQ
What is a subnet calculator?
A subnet calculator takes an IPv4 address and a CIDR prefix (like /24 or /26) and returns the network address, broadcast address, subnet mask, wildcard mask, usable host range, and total host count. It is the fastest way to verify subnetting math on the CCNA or CCNP exam, or in real network design work.
How do I calculate a subnet by hand?
Convert the CIDR to a host-bit count (32 minus the prefix length), then read the mask block size from the relevant octet. The network address is the IP with all host bits set to 0. The broadcast address has all host bits set to 1. Usable hosts are everything between, exclusive of network and broadcast. Our subnetting guide walks the full method.
What is the difference between a /24 and a /25?
A /24 has 256 total addresses and 254 usable hosts. A /25 splits that /24 in half: two /25 subnets, each with 128 addresses and 126 usable hosts. The first /25 starts at .0; the second /25 starts at .128. The block size in the fourth octet is 256 minus the mask, so a /25 has block size 128.
Does this subnet calculator support IPv6?
Not yet. This tool is IPv4-only. IPv6 subnetting follows different conventions (prefix lengths in /48, /56, /64 are common; no broadcast address) and we will ship a separate IPv6 helper. For IPv6 fundamentals, see the IPv6 section of our subnetting guide.
Are .0 and .255 always reserved?
Only inside a /24 or larger. The lowest address in any subnet is the network address; the highest is the broadcast. In a /26 from 192.168.1.0 to 192.168.1.63, the reserved addresses are .0 and .63, not .0 and .255. The /31 prefix is a special case used for point-to-point links where both addresses are usable (RFC 3021).
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation writes a subnet as an IP address followed by a slash and a prefix length, like 192.168.1.0/24. The prefix length tells you how many bits identify the network; the remaining bits identify hosts. CIDR replaced the older Class A/B/C system in 1993.
Want to master subnetting end-to-end?
Subnetting is one topic on the CCNA exam, and the topic that trips most students. CISNET's live online CCNA bootcamp covers it in week one with hands-on labs and the in-your-head fast method.
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