About CIDR Calculator

Calculate network address, broadcast, host range from CIDR notation. Part of the DevTools Surf developer suite. Browse more tools in the Networking collection.

Use Cases

• Plan VPC subnets for AWS or GCP cloud deployments
• Calculate usable host ranges for network documentation
• Verify firewall rules reference the correct IP ranges
• Design IP allocation schemes for multi-tenant environments

Tips

• Enter a CIDR block to see the full host range instantly
• Compare subnet sizes by adjusting the prefix length
• View the broadcast and network addresses for any subnet

Fun Facts

• CIDR (Classless Inter-Domain Routing) was introduced in 1993 via RFC 1519 to slow the exhaustion of IPv4 addresses by replacing classful networking.
• A /32 subnet contains exactly one IP address, while a /0 represents the entire IPv4 address space of 4,294,967,296 addresses.
• The last unallocated IPv4 /8 blocks were distributed by IANA on February 3, 2011, marking the official exhaustion of the IPv4 free pool.

FAQ

What does it show?

Network address, broadcast address, first/last host, total host count, wildcard mask, and subnet mask. Everything you need to design or audit a network.

IPv4 and IPv6?

Both. IPv6 CIDR ranges have enormous host counts — displayed in scientific notation so you know what you're dealing with.

Why does /0 give 4 billion hosts?

It matches everything. /8 gives 16M, /16 gives 65k, /24 gives 256, /32 is one host. Smaller number = larger range.

Does it check if my subnet fits my provider's rules?

No — providers impose their own CIDR constraints (AWS VPC needs /28 to /16). The tool does math; the rules are provider-specific.