IP & Network

IP Calculator

CIDR, subnets, masks and address ranges at your fingertips.

IP address with CIDR IPv4 or IPv6 with optional /prefix. Default: /32 for v4, /128 for v6.

Try: 192.168.1.0/24 10.0.0.0/8 172.16.5.0/30 2001:db8::/64

About this tool

An IP calculator turns a CIDR notation like 192.168.1.0/24 into the underlying network details: network address, broadcast address, first and last usable host, subnet mask in dotted-decimal and inverse (wildcard) form, total addresses, usable hosts, and the binary representation of the mask. It works for both IPv4 and IPv6 — for IPv6 we show prefix length, /64 sub-block counts, and EUI-64 derivation where relevant.

Beyond the basic decode, the tool can split a CIDR into smaller subnets (VLSM) or aggregate adjacent subnets back into a single supernet. Enter a parent block and a desired prefix length to get the list of contained subnets, or paste several CIDRs to find the smallest covering prefix. All math runs entirely in your browser — nothing is sent to our servers.

When to use this tool

Designing a network. Plan VLAN sizes, point-to-point links, and DHCP scopes without writing the math on paper.
Verifying firewall rules. Confirm that 10.0.0.0/8 really covers 10.5.42.7 before pushing an ACL.
Cloud subnetting. AWS, GCP and Azure all use CIDR — slice a /16 VPC into per-AZ /24 subnets in seconds.
IPv6 planning. See how a /48 from your ISP carves into /64 assignments per VLAN — there are 65,536 of them, more than you will ever need.

About usable hosts

For IPv4, the network address (.0) and broadcast address (.255 on a /24) are reserved — so a /24 has 256 total but only 254 usable hosts. Point-to-point links (/31) and host routes (/32) are special cases defined in RFC 3021 — both addresses are usable on a /31. IPv6 has no broadcast and no reserved addresses inside a /64; all 2^64 addresses are technically usable, though anything above a /64 violates SLAAC and most operating systems.

Frequently asked questions

What is CIDR notation?

CIDR (Classless Inter-Domain Routing) writes an IP block as address/prefix-length. 192.168.1.0/24 means "the 24-bit network starting at 192.168.1.0" — equivalent to the old class-C subnet mask 255.255.255.0. CIDR replaced the rigid class A/B/C system in 1993 and is now the only address-block notation used in routers, firewalls, and cloud consoles.

Why does my /24 only have 254 hosts, not 256?

The first and last addresses in any IPv4 subnet are reserved: .0 is the network address (used in routing entries), .255 is the directed broadcast. You can never assign those two to a host on a regular LAN. A /24 has 2^8 = 256 addresses minus those two = 254 usable. The exception is /31 (RFC 3021) where both ends are usable for point-to-point links.

Can I subnet IPv6 the same way?

Yes, but the conventions are different. IPv6 has no broadcast and no reserved addresses, so a /126 point-to-point or /127 link gives all addresses to hosts. The expected end-user assignment is a /64 — anything smaller (e.g. /80, /96) breaks SLAAC autoconfiguration in most operating systems. ISPs typically delegate /48 or /56 to customers.

What is a wildcard mask?

The wildcard (inverse) mask is the bitwise complement of the subnet mask. For /24 the mask is 255.255.255.0, the wildcard is 0.0.0.255. Cisco ACLs use wildcard masks — "match anywhere a 1 bit appears" — so access-list 1 permit 192.168.1.0 0.0.0.255 is the wildcard equivalent of "permit 192.168.1.0/24". Other vendors (Juniper, Fortinet) use the regular mask.