ToolsOps

Networking

CIDR and IPv4 Subnet Calculator

Enter a CIDR expression (e.g. 192.168.1.0/24) and instantly get the subnet mask, wildcard mask, network address, broadcast, first and last usable IPs, total addresses and binary representation. Supports /0–/32 including special cases like /31 (RFC 3021) and /32. Everything runs in your browser — the input is never sent to a server.

Quick examples

Result

IP address
192.168.1.123
CIDR prefix
/24
Subnet mask
255.255.255.0
Wildcard mask
0.0.0.255
Network address
192.168.1.0
Broadcast address
192.168.1.255
First usable IP
192.168.1.1
Last usable IP
192.168.1.254
Total addresses
256
Usable hosts
254
Range start
192.168.1.0
Range end
192.168.1.255

Examples

  • 192.168.1.123/24Arbitrary IP inside a /24
  • 192.168.1.0/24Typical home/office private network
  • 10.0.0.0/8Large private network
  • 172.16.5.10/20Subnet inside a private space
  • 192.168.1.10/32Single host (application loopback)
  • 10.0.0.0/31Point-to-point link (RFC 3021)

Frequently asked questions

What is CIDR?
CIDR (Classless Inter-Domain Routing) is the modern notation for describing IP networks. It combines the address with the prefix length (e.g. /24) indicating how many bits identify the network. It replaced the older A/B/C class system.
What is a subnet mask?
A subnet mask (e.g. 255.255.255.0) has 1s for the bits that identify the network and 0s for the host bits. For /24 that's 24 ones and 8 zeros. ANDing an IP with the mask yields the network address.
What is the wildcard mask?
It's the bitwise complement of the subnet mask: 1s mark the free host bits. Cisco ACLs and OSPF use the wildcard mask instead of the subnet mask. For /24 the wildcard is 0.0.0.255.
What's the difference between network address and broadcast?
The network address identifies the whole network (all host bits 0). The broadcast reaches every host in that network (all host bits 1). In /<=30 neither is assigned to a specific host.
How do I read /24?
/24 means the first 24 bits identify the network and the last 8 are the host. In 192.168.1.0/24 the network is 192.168.1.0 and there are 254 usable hosts, from 192.168.1.1 to 192.168.1.254 (192.168.1.255 is the broadcast).
What happens with /31 and /32?
/32 represents a single host: one address, no network or broadcast. /31 is a special case (RFC 3021) used on point-to-point links: only 2 addresses and both are usable, because no network or broadcast is reserved.
Does this tool send my CIDR expression to a server?
No. All the computation happens inside your browser. There are no backend calls, nothing is stored in localStorage, and everything disappears when you close the tab.