CIDR Notation Converter

Four IPv4 conversions in bulk: CIDR to IP range, IP range to minimum CIDR blocks, netmask to/from CIDR, and wildcard to CIDR. Paste one entry per line, export CSV.

Greedy algorithm: at each step find the largest CIDR aligned to the start and fitting the remaining range. Produces the minimum set of CIDRs exactly covering the range — useful for firewall rules and ACLs.

Subnet Calculator analyzes a single subnet in depth. CIDR Converter is optimized for bulk conversion and range-to-CIDR aggregation, accepting many entries at once.

Yes, the CIDR Notation Converter is 100% free with no registration, no hidden fees, and no usage limits. All processing happens locally in your browser, ensuring complete privacy.

Absolutely. The CIDR Notation Converter processes everything client-side in your browser. No data is uploaded to or stored on any server. Your content remains private on your device at all times.

Yes, the CIDR Notation Converter is fully responsive and works on smartphones and tablets. You can use it on any device with a modern web browser -- no app download required.

No account or registration is needed. Simply open the CIDR Notation Converter in your browser and start using it immediately. There are no sign-up walls or usage restrictions.

Simply enter your input in the provided field, adjust any settings to your preference, and the tool will process it instantly. You can then copy the result to your clipboard or download it.

The CIDR Notation Converter works in all modern browsers including Chrome, Firefox, Safari, Edge, and Opera. For the best experience, use the latest version of your preferred browser.

The number of addresses in an IPv4 CIDR block is 2 to the power of (32 minus the prefix length). A /24 fixes 24 bits and leaves 8 for hosts, giving 2^8 = 256 total addresses; a /16 leaves 16 host bits for 2^16 = 65,536 addresses. Each step down in prefix doubles the size: /25 holds 128, /23 holds 512, and so on. Of those, two addresses are usually reserved — the network address and the broadcast address — so a /24 offers 254 usable hosts rather than 256. This tool's CIDR to Range tab does the math for you, reporting the network, broadcast, first and last usable host, total addresses, and usable count for every block you paste. Enter your prefixes one per line to see all the figures at once.

A subnet mask and a wildcard mask describe the same network boundary but are bitwise inverses of each other. A subnet mask like 255.255.255.0 has 1-bits for the network portion and 0-bits for hosts, and it is what you type into most operating systems and routers. A wildcard mask, 0.0.0.255, flips every bit and is the form Cisco ACLs and OSPF configurations expect. Both correspond to a /24 prefix, just written differently. The common mistake is pasting a netmask where a wildcard is required, which silently matches the wrong addresses. This converter shows the netmask, wildcard, and CIDR prefix side by side so you can copy the exact form each system needs. Use the Netmask to CIDR and Wildcard to CIDR tabs to translate between all three notations instantly.

A single CIDR block can only represent ranges whose size is a power of two and whose start address is aligned to that size. An arbitrary start-to-end range rarely meets both conditions, so it must be split into several aligned blocks that together cover it exactly. For example, 192.168.1.10 to 192.168.1.20 cannot be one block, but it can be expressed as a few smaller CIDRs with no addresses spilling outside the range. The Range to CIDR tab uses a greedy algorithm: at each step it picks the largest block aligned to the current start that still fits, then advances. This yields the minimum number of blocks, keeping firewall rules and routing tables short. Paste a start and end range to see the smallest exact CIDR set.

A /32 represents a single host address, so it has exactly one usable IP and is commonly used for loopback interfaces, host routes, and pinning one machine in a firewall rule. A /31 is a special case defined by RFC 3021 for point-to-point links: instead of wasting two of its four-bit-wide pair on network and broadcast, both addresses are usable, giving two usable hosts. For every larger block the usual rule applies — total addresses minus the network and broadcast leaves the usable count, so a /30 yields four addresses but only two usable hosts. This converter handles these edge cases correctly, reporting one usable host for a /32 and two for a /31 rather than zero. Paste any prefix into the CIDR to Range tab to confirm the exact usable count.

A valid IPv4 subnet mask must be a clean run of 1-bits followed by a clean run of 0-bits, with no gaps — for example 255.255.255.0 is 24 ones then 8 zeros. A non-contiguous mask is one where the set bits are interrupted, such as 255.0.255.0, which mixes ones and zeros in a way that has no corresponding CIDR prefix length. Masks like this cannot be expressed as a /n value and are rejected by virtually all modern routing equipment, so the converter flags them rather than producing a misleading result. The same validation applies to wildcard masks, which must be contiguous after inversion. If you see this error, check for a typo or a value that was meant to be a different octet pattern. The tool validates every line as you paste, so invalid entries are caught immediately.