Reverse IP Lookup Calculator
Generate the reverse DNS (PTR) lookup format for an IPv4 or IPv6 address.
About Reverse IP Lookup Calculator
Reverse DNS maps an IP address to a hostname using PTR records in the .in-addr.arpa domain. The IPv4 address octets are reversed (since DNS hierarchy reads right-to-left but IP addresses read left-to-right) and appended with .in-addr.arpa to form the lookup name.
Formula
PTR record format
PTR = D.C.B.A.in-addr.arpa for IP A.B.C.D
- A.B.C.D
- Original IPv4 address in dotted notation
Worked example
With the default values below, Reverse IP Lookup Calculator returns PTR Record Name of 100.1.168.192.in-addr.arpa. Change any input above and every figure here is recalculated in your browser.
Inputs used
- IP Address (IPv4)
- 192.168.1.100
Results
- PTR Record Name
- 100.1.168.192.in-addr.arpa
- Reversed Octets
- 100.1.168.192
Step by step
- 1Original octets= 192.168.1.100
- 2Reverse octet order= 100.1.168.192
- 3Append arpa domain= 100.1.168.192.in-addr.arpa
Assumptions and limits
- The result is derived only from the single input listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
Why are the octets reversed?
DNS is hierarchical from right to left (e.g. .com > example.com > www.example.com) while IP addresses are hierarchical from left to right. Reversing the octets aligns IP hierarchy with DNS hierarchy, allowing delegated zone management per octet boundary.
What is a PTR record used for?
PTR records map IP addresses to hostnames — used by email servers for sender verification (SPF/DKIM), by log analysis tools for readable names, and by security tools for identifying devices by hostname from captured IP addresses.