Free tool
NetworkingSubnet Mask Calculator
Free subnet mask calculator for CCNA students and network admins. Convert CIDR to a dotted mask, see host counts, and calculate network and broadcast addresses.
Runs in your browser — your data stays on your device
Free toolA subnet mask and a CIDR prefix describe the same boundary in two formats. Windows still asks for 255.255.255.0. Cloud and Cisco screens often show /24. This free subnet mask calculator converts either way, shows the binary mask, counts usable hosts, and when you add an IPv4 address, calculates network and broadcast addresses for real subnetting practice. We built it for beginners through to network engineers who need a quick, accurate check before they configure a LAN or a lab topology.
How to use the Subnet Mask Calculator
- 1
Enter a dotted subnet mask such as 255.255.255.0, or a CIDR prefix such as /24.
- 2
Optionally enter an IPv4 address if you also want the network ID, broadcast, and usable host range.
- 3
Use the example chips to jump between common masks used in home networks and CCNA labs.
Why subnet mask conversion still matters
Exams and production gear mix formats. If you only memorise /24, a question that shows 255.255.255.192 will slow you down. The same gap shows up in network administration when one document lists CIDR and another lists dotted masks. Practising both formats, and confirming host capacity for each mask, is one of the fastest ways to tighten Cisco networking and IT student skills without waiting for a classroom whiteboard.
IPv4 subnet mask example
Enter mask 255.255.255.192 (or /26) with address 192.168.10.0. You get CIDR /26, 62 usable hosts, network 192.168.10.0, and broadcast 192.168.10.63. Compare that with /24 (255.255.255.0 → 254 hosts) and you will see why mask choice is really a size choice, not a decoration on the interface config.
Guides and next steps
Privacy note
Mask conversion runs in your browser only. We do not upload your addresses or masks.
Frequently asked questions
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