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

10.0.0.0/8

IPv4 Address class: A

Network address

10.0.0.0

Broadcast address

10.255.255.255

First host

10.0.0.1

Last host

10.255.255.254

Total addresses

16777216

Usable hosts

16777214

Prefix length

Subnet mask

255.0.0.0

Wildcard mask

0.255.255.255

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.