CIDR Calculator
The CIDR calculator converts a prefix length (from /0 to /32) into everything you need for subnet planning: the dotted-decimal subnet mask, its binary representation, the wildcard mask used in access lists, and the number of hosts the block contains.
Prefix lengths are the shorthand behind every IPv4 allocation, and being able to move between /24, 255.255.255.0, and 256 addresses without thinking is a core skill. This tool does the conversion for you and shows the binary form so the relationship between the prefix and the mask is easy to see.
CIDR Calculator
Get subnet mask, host count, and binary notation from a CIDR prefix.
Enter values above to see results.
Frequently Asked Questions
How many usable addresses are in a /24?
A /24 contains 256 total addresses, of which 254 are usable. The network address (e.g. 192.168.1.0) and the broadcast address (192.168.1.255) are reserved.
What is a wildcard mask?
A wildcard mask is the bitwise inverse of a subnet mask, used in Cisco access lists and routing filters. For a /24, the subnet mask 255.255.255.0 has the wildcard mask 0.0.0.255, which means the last octet can vary.
Read More
Guides that go deeper on the same topic.
Subnetting Guide for Network Engineers
A practical subnetting guide for network engineers covering CIDR notation, subnet plan design, VLAN and VRF mapping, common pitfalls, and tools for keeping your IP space organized at scale.
IP Planning: The Complete Guide, Tools, and Best Practices
Your network grows every week, and so does the number of IP addresses you need to track. This guide covers IP planning best practices, core concepts, and how to choose the right approach for your team.
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