Skip to content
TypeParser
All tools

IP / CIDR Calculator

Parse CIDR, get usable hosts, mask, broadcast.

beats ipaddressguide.com edge: IPv4 + IPv6 + RFC 1918 detection
CIDR
presets
analysisenter CIDR
Guide

About IP / CIDR Calculator

Parse any CIDR like <code>10.0.0.0/16</code> and get network address, broadcast, usable host range, total and usable counts, netmask, wildcard, and a per-octet binary breakdown. Detects RFC 1918 private ranges, link-local, multicast, and loopback. Basic IPv6 support including ULA / link-local detection.

What CIDR notation says

10.0.0.0/16 says “this network and the next 65,535 addresses.” The /16 is the prefix length — the count of leading bits that match the network address. Everything after that varies, those addresses are hosts within the network.

The notation collapses several legacy concepts (Class A/B/C, fixed netmasks) into one number. Modern routing, AWS VPC, Kubernetes pod networks, Google Cloud subnets — all CIDR.

What the calculator gives you

FieldExample for 10.0.0.0/16
Network10.0.0.0
Broadcast10.0.255.255
First host10.0.0.1
Last host10.0.255.254
Total addresses65,536
Usable hosts65,534
Netmask255.255.0.0
Wildcard0.0.255.255
ClassRFC 1918 private
Binaryfull per-octet breakdown

Common workflows

Plan an AWS VPC. Pick a /16, split into AZ-aligned /20s. The subnet split panel hands you each subnet’s bounds without paper math.

Verify a security-group source. Paste the source CIDR, confirm the host range matches what you expect to allow.

Audit a firewall rule. A rule allowing 0.0.0.0/0 is “everything.” 10.0.0.0/8 is your private range. 192.168.1.0/24 is one local net. The breakdown makes intent obvious.

Convert legacy netmasks. Some old gear takes 255.255.255.0 not /24. Both directions work — paste either, get both.

Sanity-check a peering range. Two networks that overlap fail to peer. Paste both CIDRs, eyeball the bounds, fix before deploying.

Why CIDR is everywhere

CIDR (Classless Inter-Domain Routing, RFC 4632) replaced fixed-width address classes in 1993. It scaled IPv4 by another 25 years, became the lingua franca for cloud subnetting, and survives unchanged in IPv6. Knowing how to read it cold pays back forever.

Frequently asked questions

What is "usable hosts" vs total?
In a /24, you have 256 addresses but only 254 usable hosts — first address is the network identifier, last is the broadcast. For /31 point-to-point links the rules differ (RFC 3021), and /32 is a single host. The calculator shows both numbers.
How does RFC 1918 detection work?
We check the input against the three reserved private ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) plus carrier-grade NAT (100.64.0.0/10) and link-local (169.254.0.0/16). The badge at the top shows what class your address falls into.
What is a wildcard mask?
The bitwise inverse of the netmask. ACLs in Cisco gear and some AWS components use wildcard rather than netmask. /24 netmask is 255.255.255.0; wildcard is 0.0.0.255.
Does it support IPv6?
Yes — basic. We parse compressed notation (fe80::/10), compute network and host portions, detect ULA fc00::/7, link-local fe80::/10, multicast ff00::/8, and loopback. The /128 single-host case is handled.
How do I split a /16 into /24s?
Toggle Subnet split. Pick the target prefix — e.g. /24 from a /16 gives 256 subnets. The list panel shows each subnet's network and broadcast.
Why does my AWS VPC reject a /24?
AWS VPC requires /16 to /28. /24 fits inside, but you cannot create a VPC at /24 — only subnets within. The calculator does not check provider constraints; verify against your cloud's docs.

Related tools

Last updated: 2025-01-15