CIDR Calculator

Subnet & IP Range Tool — network address, broadcast, hosts, binary visualizer, VLSM & more

CIDR Calculator

Subnetting
Supernetting
VLSM
Subnet Table

Subnet a /24

Split a /24 network into smaller subnets.

Supernetting

Combine subnets into a larger supernetwork. Enter one CIDR per line.

VLSM Subnetting

Allocate subnets of varying sizes from a base network.

Common Subnet Reference Table

CIDRSubnet MaskWildcardTotal AddressesUsable HostsClass

Features

🔢

Full CIDR Calculation

Network address, broadcast, first/last usable, total and usable host counts, subnet mask, wildcard mask, and binary representation at a glance.

📊

Visual Binary Display

See every bit of the IP address with network and host portions highlighted in distinct colors so you instantly grasp the subnet boundary.

📐

VLSM Support

Allocate variable-length subnets from a single base network — enter each subnet's name and required host count, and get an optimal allocation plan.

🔀

Subnet & Supernet

Split any network into smaller subnets or combine multiple subnets into a supernet with one click.

Frequently Asked Questions

What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation expresses an IP network as an address followed by a slash and a prefix length, e.g. 192.168.1.0/24. The prefix length (0–32 for IPv4) indicates how many leading bits are the network portion. The remaining bits identify hosts within that network.
How do I determine the number of usable hosts?
For a /N prefix, the total addresses are 2(32−N). Two addresses are reserved — the network address (all host bits zero) and the broadcast address (all host bits one) — so the usable hosts are 2(32−N) − 2. For /31 (point-to-point links, RFC 3021) and /32 (single host), special rules apply: /31 yields 2 usable addresses and /32 yields 1.
What is VLSM and when should I use it?
Variable Length Subnet Masking (VLSM) lets you allocate subnets of different sizes from a single network. Instead of dividing a network into equal-sized subnets, VLSM allocates each subnet just enough address space for its needs, minimizing waste. Use it when designing networks with links of varying sizes (e.g. a large LAN, a small point-to-point link, and a medium-sized department VLAN sharing one block).

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