CIDR to IP Range — IPv4 Range Expander & IP Range Calculator Online

CIDR to IP Range — IPv4 Range Expander & IP Range Calculator Online. Free online CIDR to IP range expander.

Find the CIDR block covering a start and end IPv4 address, or expand a CIDR block or IP range into the full list of addresses, instantly in your browser.

Convert any CIDR to IP range and expand IPv4 address ranges instantly with our free online IP range calculator.

Enter start and end IPv4 addresses to get the CIDR notation, aligned subnet boundaries, total address count, and the valid CIDR range, or expand a CIDR block or start-end range into the list of every IP address (up to 65,536 per list) — all computed in your browser with no data sent to any server.

Essential for network engineers, sysadmins, and security professionals configuring firewalls, ACLs, or cloud security groups.

Our CIDR range expander and ip range calculator automatically aligns your IP range to the nearest valid subnet boundary, giving you the correct CIDR block notation for any address pair.

Perfect for translating firewall policy ranges into CIDR notation, turning an IP range to a list for scanners and allow-lists, validating subnets, or planning IP address allocations.

Use it alongside our IPv4 Subnet Calculator and IPv4 Address Converter for a complete CIDR calculator toolkit.

Frequently asked questions

How do I calculate the CIDR notation for an IP range?

Type the Start IPv4 Address and End IPv4 Address, for example 192.168.1.1 and 192.168.6.255. The table compares your input with the calculated subnet: start and end address, addresses in range and the CIDR notation, here 192.168.0.0/21. Click any value to copy it.

Why is the calculated range bigger than the one I entered?

A single CIDR block must start on a boundary and contain a power of two addresses, so the tool expands your range to the smallest block that includes both addresses. The Addresses in Range row shows your original count next to the size of the expanded subnet.

Can I expand a CIDR like 10.0.0.0/24 into a list of IP addresses?

Yes. Type the block, for example 10.0.0.0/24, or a range such as 10.0.0.1-10.0.0.20 into the CIDR block or IP range field. Every address appears one per line, from the network address to the last one, with Copy list and Download .txt buttons. Lists stop after 65,536 addresses, a full /16, and a note shows the real total.

What does the Invalid Range Combination error mean?

It appears when the start address is higher than the end address. Click Switch Addresses to swap the two fields, or correct the addresses so that the start is less than or equal to the end.

What does CIDR notation mean?

CIDR notation writes a network as its first address, a slash and the prefix length, which is the number of fixed leading bits. A /24 contains 256 addresses and a /21 contains 2,048; each step down in prefix length doubles the size.

How to use this online tool

CIDR to IP Range — IPv4 Range Expander & IP Range Calculator Online is designed for fast browser workflows when you need to format, validate, convert, decode, encode, generate, or inspect data without opening a heavy desktop app. Start with the input field or visible options, review the result, then copy or download the output for the next step.

Private processing in your browser

CIDR to IP Range — IPv4 Range Expander & IP Range Calculator Online keeps the normal processing step local in your browser. That is useful for code snippets, tokens, documents, configuration values, text samples, and other material that should not be sent to a remote service unless you explicitly choose to share it.

When this tool is useful

Use CIDR to IP Range — IPv4 Range Expander & IP Range Calculator Online for repeatable developer tasks, technical documentation, QA checks, quick conversions, debugging, content cleanup, and internal team workflows. The page focuses on clear inputs, immediate feedback, and output that is easy to reuse in code, reports, tickets, emails, or notes.

Practical tips

Before copying the final result, check important details such as spacing, casing, filenames, encoding, token structure, line breaks, or output format. Small checks prevent mistakes when the result is reused in source code, API requests, documentation, spreadsheets, or shared files.