Subnet Calculator
WEBCalculate network and broadcast addresses, masks, host ranges and counts from an IP and CIDR — free in your browser.
What is the Subnet Calculator tool?
Subnet calculator turns an IP address and a CIDR prefix into everything you need to know about the network: the network and broadcast addresses, the subnet mask and wildcard mask, the first and last usable host, and the total host count. Type 192.168.1.0/24 and the whole picture appears instantly — a free IP subnet calculator that recalculates as you type, with no button to press and no sign-up.
It is built for the people who actually do subnetting: CCNA and networking students checking homework against a reliable answer, admins carving an address plan into smaller subnets, and anyone who just needs a quick CIDR-to-netmask conversion. The classic reference points are all one keystroke away — a /24 is mask 255.255.255.0 with 254 usable hosts, a /30 leaves exactly 2 hosts for a point-to-point link, and a /16 opens up 65,534 addresses. Change the prefix and watch every derived value update, which is the fastest way to build intuition for how subnet masks work.
Everything is calculated on your device. The subnetting math is pure client-side code, so no IP you type is ever sent to a server — nothing leaves your browser, and once the page has loaded the calculator even works offline. It is fully usable on a phone, which makes it a handy pocket reference during labs and exams where a full workstation is not around.
How to use the Subnet Calculator
- Enter an IPv4 address — for example 192.168.1.10.
- Set the CIDR prefix (like /24) or pick the subnet mask you want to test.
- Read the results instantly: network address, broadcast address, subnet mask and wildcard mask.
- Check the usable host range — the first and last assignable addresses — and the total host count.
- Adjust the prefix up or down to compare subnet sizes; every value recalculates as you type.
Frequently asked questions
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation writes a network as an address plus a prefix length, like 192.168.1.0/24. The /24 means the first 24 bits identify the network and the remaining 8 bits identify hosts — which is exactly the information a subnet mask encodes, just shorter.
How many usable hosts are in a /24?
254. A /24 contains 256 addresses, but the first is the network address and the last is the broadcast address, leaving 254 for devices. The general rule is 2^(32 − prefix) − 2 usable hosts — so a /26 gives 62, a /27 gives 30 and a /30 gives 2.
What is the difference between the network address and the broadcast address?
The network address is the first address of a subnet and identifies the subnet itself — no device can use it. The broadcast address is the last one, used to reach every host in the subnet at once. Everything between the two is the usable host range.
How do I calculate a subnet by hand?
Work in powers of two: the prefix tells you how many bits belong to the network, and 32 minus the prefix gives the host bits. 2 to the power of the host bits is the block size; subtract 2 for the network and broadcast addresses to get usable hosts. This calculator is a quick way to verify your manual work while you practise.
What is a wildcard mask and why does it matter?
A wildcard mask is the bit-inverse of the subnet mask — 255.255.255.0 becomes 0.0.0.255. Cisco ACLs and OSPF configuration expect wildcard masks instead of subnet masks, which is why the calculator shows both side by side.
Does this subnet calculator support IPv6?
No — it is an IPv4 subnet calculator, covering prefixes from /0 to /32. IPv6 subnetting follows different conventions (no broadcast address, /64 as the standard subnet size), so it deserves a dedicated tool rather than a bolted-on mode.
Is it free, and is anything sent to a server?
Free with no sign-up and no limits — and no, nothing is sent anywhere. All subnet math runs in your browser on your device, so the addresses you type never leave it. That also means the calculator keeps working offline once the page is open.
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