CIDR Prefix & Subnet Mask Converter
Convert IPv4 CIDR prefixes and contiguous subnet masks in either direction, with the address count.
What this tool calculates
CIDR Prefix & Subnet Mask Converter is designed to give a direct answer from the values entered above. The main inputs on this page are CIDR prefix or subnet mask. The result is intended to be readable immediately, with the explanation below available when you need to verify the method.
Method and calculation basis
CIDR /n means the first n bits are the network prefix. The subnet mask is those network bits set to 1 followed by host bits set to 0. Network and broadcast addresses come from applying the mask to the IPv4 address and host range.
Worked examples
192.168.1.10/24
Mask 255.255.255.0, network 192.168.1.0 and broadcast 192.168.1.255.
A /30 link
A /30 contains four addresses in total; conventional IPv4 subnetting leaves two host addresses.
Understanding the result
The output should be read in the units shown beside the result. If you are comparing alternatives, keep all unchanged assumptions identical and alter one input at a time. That makes it easier to see which value is responsible for the difference.
Assumptions, edge cases and accuracy
Address arithmetic does not prove reachability. Routing, VLANs, NAT, DNS, host configuration and firewall policy can all change what actually works on a network.
Sources and methodology
- IETF RFCs — Internet addressing, CIDR and protocol definitions
- IANA — Protocol parameters, port/service registries and address information
Method reviewed for Instant Solvers V10.0 · October 2026. If you find a calculation or explanation that needs correcting, use the site Contact page and include the tool URL and the values you entered.