CIDR / Subnet Calculator
Analyze a CIDR range or split it into variable-size child subnets (VLSM)
Enter a CIDR expression or IP address to see subnet details
Uses BigInt math for IPv4 (/0–/32) and IPv6 (/0–/128). Split mode packs largest-first into the parent and decomposes leftover space into valid CIDR blocks. All processing happens locally in your browser.
About CIDR / Subnet Calculator
Calculate IPv4 and IPv6 subnet ranges, network addresses, broadcast addresses, netmasks, wildcard masks, and host counts directly in your browser. CIDR (Classless Inter-Domain Routing) notation is the standard way to describe network ranges in modern networking, used in routing tables, firewall rules, cloud security groups, VPC configurations, and Kubernetes networking. This tool accepts a CIDR expression like 192.168.1.0/24 or 2001:db8::/32 and produces every value you need to plan a subnet, validate a firewall rule, or audit a network design. All math runs locally using arbitrary-precision BigInt — your network topology never leaves your device.
How to Use CIDR / Subnet Calculator
- Enter a CIDR expression (e.g. 192.168.1.0/24) or a bare IP address.
- View the network address, broadcast, host range, masks, and address counts instantly.
- Use the preset buttons for common ranges like 10.0.0.0/8 or fe80::/10.
- Copy individual values or the full summary using the copy buttons.
CIDR / Subnet Calculator FAQ
Does this support IPv6?
Yes. The calculator handles both IPv4 (/0–/32) and IPv6 (/0–/128) using BigInt math, including IPv6 :: compression, embedded IPv4 addresses, and link-local detection.
What does /24 mean in CIDR notation?
The /24 suffix means the first 24 bits of the address are the network portion, leaving 8 bits for hosts. In IPv4 this gives 256 total addresses (254 usable hosts after reserving network and broadcast).
Why are /31 and /32 prefixes special?
A /32 represents a single host address. A /31 represents a 2-address point-to-point link where both addresses are usable (per RFC 3021), so the calculator does not subtract network and broadcast for these prefixes.
What is the wildcard mask used for?
Wildcard masks (the inverse of a netmask) are used in Cisco access control lists and OSPF area definitions, where they specify which bits the router should ignore when matching addresses.
Is my input sent to a server?
No. All CIDR parsing and subnet math runs locally in your browser using BigInt arithmetic. Nothing is transmitted.