IP Subnet Calculator
Enter an IPv4 address and CIDR prefix to get the network address, subnet mask, usable host range, host count and broadcast address.
Last updated: October 2026
Subnet details
Network 192.168.1.0/24 · Mask 255.255.255.0 · Hosts 192.168.1.1 – 192.168.1.254 (254 usable) · Broadcast 192.168.1.255
Formula below · 1 source (rfc-editor.org) · Updated Oct 2026
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About this calculator
An IPv4 address has 32 bits. A CIDR prefix such as /24 says the first 24 bits name the network and the remaining 32 − 24 = 8 bits number the hosts inside it, so the block holds 2⁸ = 256 addresses.
What the calculator works out
Subnet mask: the prefix written as 1-bits followed by 0-bits, in dotted decimal. /24 is 255.255.255.0 and /26 is 255.255.255.192. Network address: your address with all host bits set to 0 (the address AND the mask). 192.168.1.10/24 is in network 192.168.1.0. Broadcast address: the network with all host bits set to 1, here 192.168.1.255. Usable hosts: everything between the two, 192.168.1.1 to 192.168.1.254, which is 2⁸ − 2 = 254 addresses.
Point-to-point links and single hosts
The −2 applies to ordinary subnets, because the network and broadcast addresses cannot be given to a device. RFC 3021 allows a /31 on point-to-point links with both addresses usable and no broadcast, and a /32 is a single host. The calculator follows those rules.
IPv6 works differently: subnets are normally /64 and there is no broadcast address, so this page covers IPv4 only.
IPv4 prefix lengths, masks and usable hosts
Scroll sideways to see all columns →
| Prefix | Subnet mask | Addresses | Usable hosts |
|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 |
| /16 | 255.255.0.0 | 65,536 | 65,534 |
| /22 | 255.255.252.0 | 1,024 | 1,022 |
| /23 | 255.255.254.0 | 512 | 510 |
| /24 | 255.255.255.0 | 256 | 254 |
| /25 | 255.255.255.128 | 128 | 126 |
| /26 | 255.255.255.192 | 64 | 62 |
| /27 | 255.255.255.224 | 32 | 30 |
| /28 | 255.255.255.240 | 16 | 14 |
| /29 | 255.255.255.248 | 8 | 6 |
| /30 | 255.255.255.252 | 4 | 2 |
| /31 | 255.255.255.254 | 2 | 2 (RFC 3021) |
| /32 | 255.255.255.255 | 1 | 1 |
How to use
Type any address in the subnet and its prefix length (the number after the slash). Example 1: 192.168.1.10 /24 → Network 192.168.1.0/24 · Mask 255.255.255.0 · Hosts 192.168.1.1 – 192.168.1.254 (254 usable) · Broadcast 192.168.1.255. Example 2: 10.20.30.77 /26 → Network 10.20.30.64/26 · Mask 255.255.255.192 · Hosts 10.20.30.65 – 10.20.30.126 (62 usable) · Broadcast 10.20.30.127. Example 3: 172.16.5.4 /30, a router-to-router link → Network 172.16.5.4/30 · Hosts 172.16.5.5 – 172.16.5.6 (2 usable) · Broadcast 172.16.5.7.
Frequently asked questions
Why are there 2 fewer usable hosts than addresses?
In a normal subnet the first address (all host bits 0) identifies the network and the last (all host bits 1) is the broadcast address, so neither can be assigned to a device. A /24 has 256 addresses and 254 usable hosts. RFC 3021 makes an exception for /31 point-to-point links.
How do I convert a CIDR prefix to a subnet mask?
Write the prefix as that many 1-bits followed by 0-bits and read it as four bytes. /26 = 11111111.11111111.11111111.11000000 = 255.255.255.192. Common ones: /8 = 255.0.0.0, /16 = 255.255.0.0, /24 = 255.255.255.0, /30 = 255.255.255.252.
How do I find the network address?
Apply a bitwise AND between the address and the mask. In the octet the mask splits, round down to a multiple of the block size: for /26 the block size is 64, so 10.20.30.77 falls in the block starting at 10.20.30.64.
Which prefix do I need for a given number of hosts?
Pick the smallest block with enough room after subtracting 2: 6 hosts → /29, 14 → /28, 30 → /27, 62 → /26, 126 → /25, 254 → /24. Leave headroom for growth.
Does this work for IPv6?
No. IPv6 addresses are 128 bits, LAN subnets are normally /64, and there is no broadcast address. This calculator handles IPv4 only.
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Sources & references
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