IP to Decimal Converter

About IP Address Converter

An IP address is a number, and it gets written in whatever form suits the place it is stored: dotted decimal in a config file, a 32-bit integer in a database column, hex in a packet capture, an IPv4-mapped IPv6 address in a dual-stack server's logs. This reads any of those forms and writes all the others.

It also says what kind of address it is, from the IANA special-purpose registries: private (RFC 1918), carrier-grade NAT, loopback, link-local, documentation, multicast, unique local IPv6, 6to4, NAT64 and the rest. It says whether the address can appear on the public internet at all, which is usually the real question behind the conversion.

IPv6 addresses are shown both compressed, as RFC 5952 specifies, and fully expanded, with the reverse-DNS name used for PTR records. An IPv4 address embedded in an IPv4-mapped, NAT64 or 6to4 address is extracted.

Where it helps

• Reads dotted, integer, hex, binary, bracketed and zone-indexed forms without being told which one it is.
• Classifies the address using the IANA special-purpose registries, including CGNAT, NAT64 and documentation ranges.
• Writes IPv6 compressed exactly as RFC 5952 specifies, and fully expanded.
• Converts in the browser with no lookup, so it works on internal addresses without sending them anywhere.

Limits

• It converts and classifies. It does not say who owns an address or where it is; IP Lookup and WHOIS do that.
• Old shorthand forms such as 10.1 or octal octets (010.0.0.1), which some parsers still accept, are rejected as ambiguous.

Frequently asked questions

How do I convert an IP address to an integer?

Multiply the first octet by 16,777,216, the second by 65,536 and the third by 256, then add all four. 192.168.1.10 is 192×16777216 + 168×65536 + 1×256 + 10 = 3232235786. Storing addresses as integers makes range queries such as "is this address inside 10.0.0.0/8" simple comparisons.

Is 100.64.x.x a private address?

Not in the RFC 1918 sense, but it is not public either. 100.64.0.0/10 is shared address space for carrier-grade NAT (RFC 6598): an ISP uses it between its own NAT and your router. Seeing it on your router's WAN side means you are behind your provider's NAT.

What does ::ffff: in front of an IPv4 address mean?

It is an IPv4-mapped IPv6 address: how a dual-stack socket represents an IPv4 client. ::ffff:203.0.113.45 is simply 203.0.113.45. Strip the prefix before comparing it with IPv4 allow-lists.

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