ipv4calc.com is a free, fast, no-account-required IPv4 subnet calculator built for anyone who works with IP networks — from seasoned network engineers to students sitting their first CCNA exam. Enter a CIDR block, get your results instantly. That's it.
The site exists because subnetting calculations are something network professionals do constantly, and doing them by hand is tedious and error-prone. A reliable, distraction-free tool that just works — with no paywalls, no sign-up forms, and no unnecessary complexity — is something worth having on the open web.
Network address, broadcast address, subnet mask, CIDR prefix, and wildcard mask from any IPv4 CIDR block.
First and last assignable host addresses, plus total and usable host counts — correctly excluding network and broadcast.
Divide any network into equal-sized subnets by entering a new (larger) prefix. Up to 1,024 subnets displayed inline.
No JavaScript frameworks, no loading spinners, no account required. Results appear on the same page the moment you submit.
The calculator is built with Python and FastAPI, using Python's built-in ipaddress module for all subnet arithmetic — no third-party networking libraries, no client-side JavaScript doing the maths. The UI is rendered server-side with Jinja2 templates and styled with Tailwind CSS. It's deliberately lightweight and fast.
If you're new to subnetting or want to understand the maths behind the results, we've put together two supporting resources:
The Subnetting Guide covers IPv4 addressing from scratch — binary representation, network classes, CIDR notation, VLSM, wildcard masks, and a fully worked subnetting example with a reference table covering /16 through /32.
The FAQ gives quick answers to the most common questions — what /24 means, how host counts work, what private IP ranges are, and how wildcard masks differ from subnet masks.
No sign-up. No limits. Just enter a CIDR block and go.
Open Calculator Read the Guide