What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation expresses an IP address and its associated network prefix length as a single string, e.g. 192.168.1.0/24. The number after the slash indicates how many leading bits define the network portion.

What is the usable host count?

In an ordinary IPv4 subnet the network address (first) and broadcast address (last) are reserved, so usable hosts = 2^(32 - prefix) - 2. A /32 is a single-host route with its one address usable; a /31 has two usable endpoint addresses for point-to-point links.

Does this tool support IPv6?

Currently only IPv4 CIDR blocks are supported. IPv6 support may be added in a future update.

What happens with /31 and /32 prefixes?

A /32 identifies one usable host address. A /31 is a two-address point-to-point link under RFC 3021, where both endpoint addresses are usable.

Is my data sent to a server?

No. All calculations happen entirely in your browser using JavaScript. No data is transmitted.

CIDR to IP Range

Enter a CIDR block and instantly see the network address, broadcast, subnet mask, IP range, and usable host count.

CIDR Block

Enter CIDR notation

Quick examples

Subnet Details

Enter a CIDR block to see results

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Summary

This tool converts any IPv4 CIDR notation (e.g. 10.0.0.0/8) into a full subnet breakdown — network address, subnet mask, broadcast address, first and last usable host, and total host count. All computation runs locally in your browser with no data sent to any server.

How it works

Enter a CIDR block in the format x.x.x.x/prefix (e.g. 192.168.1.0/24).
The tool parses the prefix length to derive the subnet mask.
It calculates the network address by applying the mask to the host address.
The broadcast address is computed as network address OR (NOT mask).
First and last usable hosts are network + 1 and broadcast - 1 respectively.
Results update instantly as you type.

Use cases

Plan IP address allocation for cloud VPCs and subnets.
Verify firewall rules that reference CIDR ranges.
Debug routing table entries that use CIDR notation.
Quickly determine how many hosts fit inside a given subnet.
Convert between CIDR prefix lengths and dotted-decimal subnet masks.
Check whether two CIDR blocks overlap before merging networks.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu