Networking Guides
Plain-English explanations of the ideas behind the tools: subnet masks, private addressing, and the network sizes you meet most often. Each guide uses worked examples and links to the tool that does the calculation for you.
Reference guides
Start here if you want a quick answer or a chart to keep open while you work.
Common network sizes
Three prefix lengths account for most of the subnets you will ever configure. Each guide lists the exact masks, ranges, and host counts, shows how to split the network into smaller ones, and covers the mistakes people make with it.
Tools that go with the guides
The guides explain the concepts and the tools do the arithmetic. Everything is free, needs no account, and the calculators run in your browser.
Suggested reading order
If you are new to subnetting, read the subnet mask cheat sheet first so the mask and prefix notation make sense, then the /24 guide, which is the network size you will meet most often. Move on to /27 to see how a /24 is divided, and /16 to see how many /24s fit into a larger block. Finish with private IP ranges, which explains why some addresses never appear on the public internet and how to avoid overlaps when you plan your own.
New guides are added regularly. If there is a topic you would like covered, email hello@netcalctools.com.