Free tool
IPv4 subnet calculator
Enter an IPv4 address with a prefix or a mask. Get the network, broadcast and host range, and see the working step by step with the block-size method. Free, right in your browser.
The tool
How it's calculated, in short
- The prefix tells you how many bits belong to the network.
/26means 26 network bits and 6 host bits, so the mask is255.255.255.192. - Find the interesting octet, where the mask ends (the fourth one here), and the block size: 256 − 192 = 64.
- Subnets start every 64: .0, .64, .128, .192. For
192.168.10.77, 77 sits between 64 and 128, so the network is192.168.10.64. - The broadcast is the address just before the next network:
192.168.10.127. Hosts run from .65 to .126, which is 2^6 − 2 = 62.
The full method, with /20, /22 and /30 examples, VLSM and practice exercises with answers, is in the guide Subnetting explained step by step.
Frequently asked questions
What does this subnet calculator do?
It takes an IPv4 address with a prefix (for example /26) or a mask (255.255.255.192) and works out the network address, broadcast, first and last host, number of usable hosts, wildcard mask and address type. It also shows the address in binary, with the network/host boundary marked.
Can it split a network into equal subnets or plan VLSM?
Yes. The “Equal subnets” tab splits a network by the number of subnets or by the hosts you need in each. The “VLSM” tab allocates blocks of different sizes, from the largest requirement to the smallest.
Why do we subtract 2 addresses in every subnet?
The first address is the network address and the last one is the broadcast; neither can be given to a device. The exceptions are /31 (point-to-point links, RFC 3021), which has 2 usable addresses, and /32, which is a single host.
Are the addresses I type sent anywhere?
No. Everything is calculated in your browser, and the addresses never leave your device.
Can I use a calculator in the CCNA exam?
No, you subnet by hand in the exam. Use the calculator to check the exercises you solve yourself; speed comes from a few minutes of practice every day.
Make subnetting second nature
The Routerel trainer gives you endless subnetting exercises with worked answers, plus 1,900+ CCNA questions with explanations.