Subnetting, made instant.
Subnet Calculator is a fast, free tool that turns any IPv4 or IPv6 network into its full addressing breakdown the moment you type it. No sign-up, no ads, and nothing leaves your browser.
Network planning shouldn't mean doing binary math by hand or trusting a page that ships your addresses off to some server. We built Subnet Calculator to be the tool we wanted ourselves: precise, immediate, and completely private.
What it does
Enter one or more networks in CIDR (10.0.0.0/24), IPv6, or IP-and-mask
form and get the network and broadcast address, usable host range, subnet mask,
wildcard mask, and host count for each: recalculated live as you type. Beyond the core
calculator, it includes:
- A VLSM subnet splitter that carves a block into right-sized subnets, largest-first, so no address space is wasted.
- A CIDR summarizer / aggregator that collapses long route lists into the fewest blocks that cover exactly the same addresses.
- Full IPv4 and IPv6 support, including address-kind detection (private, loopback, link-local, documentation and more).
Privacy by design
Every calculation runs entirely in your browser. There is no backend doing the math and no analytics tracking what you enter. Your networks, addresses and topology never leave your device. Read the full details in our Privacy Policy.
Who it's for
Network engineers sizing subnets, students learning how CIDR and masks work, and IT admins verifying a configuration under time pressure. If you work with IP addresses, this is meant to save you a few minutes and a few mistakes every day.
Questions or feedback?
We'd genuinely like to hear it. Head over to the Contact Us page and drop us a line, or just jump straight back to the calculator.