Subnet Calculator — IPv4 CIDR Subnet Mask Calculator Online
Calculate IPv4 subnet details from a CIDR notation. Get network address, broadcast address, host range, subnet mask, and number of hosts. Free, instant, runs in your browser.
Enter an IPv4 address and prefix, or use CIDR notation like 192.168.1.10/24.
Common subnet sizes
| CIDR | Subnet mask | Total | Usable hosts |
|---|---|---|---|
| /8 | 255.0.0.0 | 16,777,216 | 16,777,214 |
| /16 | 255.255.0.0 | 65,536 | 65,534 |
| /24 | 255.255.255.0 | 256 | 254 |
| /25 | 255.255.255.128 | 128 | 126 |
| /26 | 255.255.255.192 | 64 | 62 |
| /28 | 255.255.255.240 | 16 | 14 |
| /30 | 255.255.255.252 | 4 | 2 |
| /32 | 255.255.255.255 | 1 | 0 |
* Network and broadcast addresses are reserved. /31 subnets (RFC 3021) have 2 usable endpoints for point-to-point links.
What is a subnet?
A subnet divides an IP network into smaller segments. CIDR notation like 192.168.1.0/24 defines both the network and its size — the number after / is the prefix length, indicating how many bits belong to the network part.
- —Network address — first address in the subnet, identifies the network itself.
- —Broadcast address — last address, used to send packets to all hosts on the subnet.
- —Subnet mask — bitmask that separates the network and host portions of an IP.
- —Wildcard mask — inverse of the subnet mask, commonly used in ACLs and firewall rules.