Subnet Calculator
Calculate subnet details from CIDR notation — network, broadcast, host range, and more
About Subnet Calculator
A subnet divides an IP network into smaller ranges. CIDR notation, such as 192.168.1.0/24, states how many leading bits identify the network; the rest identify hosts. The prefix length determines the subnet mask, the number of usable addresses, and the first and last host.
Enter an address with a prefix length and the calculator shows the network address, broadcast address, subnet mask, host range, and total host count. It is useful when planning networks, writing firewall or security group rules, and checking that two addresses belong to the same subnet.
Common use cases
- Working out how many hosts fit in a /24, /26, or /28 subnet.
- Finding the network and broadcast address for a given IP and prefix.
- Checking that a cloud VPC or subnet plan does not overlap.
- Converting between CIDR prefix and dotted subnet mask.
Frequently asked questions
- Why are usable hosts two fewer than the total?
- In traditional IPv4 subnets one address is reserved for the network and one for broadcast. Cloud providers may reserve additional addresses.
- What does /24 mean?
- The first 24 bits are the network portion, which corresponds to the mask 255.255.255.0 and 256 addresses.
- Is my network information sent anywhere?
- No. The calculation runs in your browser.