A subnet mask calculator converts between CIDR notation (like /26) and dotted-decimal subnet masks (like 255.255.255.192), and tells you how many hosts each subnet supports. It’s a fast reference for network admins, IT certification students and anyone configuring a router.
A subnet mask uses 1s for the network bits and 0s for the host bits. A /24 mask has 24 ones: 255.255.255.0. A /26 has 26 ones: 255.255.255.192. The number of usable hosts is 2^(32 − prefix) − 2, subtracting the network and broadcast addresses. So /24 gives 254 hosts, /26 gives 62, /28 gives 14 and /30 gives 2, which is common for point-to-point links.
Quick reference for the last octet: /25 = 128, /26 = 192, /27 = 224, /28 = 240, /29 = 248, /30 = 252. The block size, which tells you where each subnet starts, is 256 minus that number: /26 subnets start at 0, 64, 128 and 192.
Tips: choose the smallest subnet that fits your hosts plus room to grow. Variable-length subnet masking (VLSM) lets you use different mask sizes within the same network to save addresses. Wildcard masks, used in some router configurations, are the inverse of subnet masks (0.0.0.63 for a /26).
Why use an online Subnet Mask Calculator: it saves time, avoids simple arithmetic mistakes and shows each step, so you can check your homework, plan a project or make a decision with confidence. Bookmark the page so it’s ready the next time you need it.
Tips for getting accurate results from the Subnet Mask Calculator: double-check that every input uses the right units, enter numbers without commas or symbols, and run the calculation a second time with a quick estimate in your head to confirm the answer looks reasonable.
Learn more on Wikipedia’s subnetwork article. Find IP subnet, hex and XOR calculators on Minedit.