What does CIDR notation mean?

CIDR (Classless Inter-Domain Routing) writes a network as address/prefix, e.g. 203.0.113.0/24. The prefix says how many leading bits are fixed; the remaining bits enumerate the addresses in the block. A /24 fixes 24 bits, leaving 8 free, so it covers 256 addresses.

Why does my IP range convert to several CIDR blocks?

A single CIDR block always covers a power-of-two number of addresses and must start on an aligned boundary. An arbitrary start-end range rarely lines up, so the converter emits the minimal set of blocks that together cover exactly the range you entered, nothing more and nothing less.

Does the converter support IPv6?

Yes. Both directions accept IPv6, e.g. 2001:db8::/32 expands to its first and last address, and an IPv6 start-end range is split into minimal CIDR blocks the same way as IPv4.

CIDR to IP Range Converter (and Range to CIDR)

CIDR block (IPv4 or IPv6)

Examples:

IP range to CIDR blocks

to

Examples:

Minimal CIDR cover

What this converter does

The top panel expands CIDR notation into the concrete range it covers: first and last address, total address count, and for IPv4 also the subnet mask, wildcard mask and usable host range. That is the direction you need when a firewall rule, WHOIS record or BGP announcement gives you 198.51.100.16/29 and you want to know exactly which addresses fall inside.

The bottom panel goes the other way. Give it any start and end address and it computes the minimal set of CIDR blocks that covers the range exactly. Access control lists, route filters and cloud security groups only accept CIDR, so an instruction like "block 203.0.113.5 through 203.0.113.94" has to be translated into blocks first; this panel does the alignment math for you. Both panels handle IPv4 and IPv6 and run entirely in your browser.

If you want deeper subnet math (network class, binary breakdown, host planning), the Subnet Calculator continues where this converter stops. To see who an address block belongs to, run it through the IP lookup.