Private vs Public IP Calculator

Work out private vs public ip instantly with clear inputs, formula shown and shareable results.

About Private vs Public IP Calculator

RFC 1918 sets aside 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 for private use; those addresses are filtered by internet routers and must be translated by NAT. Other blocks are special rather than private: 169.254.0.0/16 is link-local autoconfiguration, 127.0.0.0/8 is loopback, and 100.64.0.0/10 is carrier-grade NAT space that subscribers often mistake for public.

Formula

Range membership test

address is in block if (address AND mask(prefix)) equals the block's network address

Worked example

With the default values below, Private vs Public IP Calculator returns Address scope of Private. Change any input above and every figure here is recalculated in your browser.

Inputs used

IPv4 address: 10.45.7.9
Flag carrier-grade NAT space (100.64.0.0/10)one of Yes, No: Yes

Results

Address scope: Private
Matched reserved range: 10.0.0.0/8 - RFC 1918 private
NAT required for internet access: Yes - needs NAT or a proxy to reach the internet
Globally routable: No

Step by step

1Values used
2Range membership test
3Address scope= Private
4Matched reserved range= 10.0.0.0/8 - RFC 1918 private
5NAT required for internet access= Yes - needs NAT or a proxy to reach the internet
6Globally routable= No

Assumptions and limits

The result is derived only from the 2 inputs 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

Can I use private addresses on the internet?

No. Providers drop RFC 1918 sources and destinations, so traffic must be translated to a public address at the edge.

Why does my router show a 100.64.x.x WAN address?

That is carrier-grade NAT. The provider is sharing public addresses across subscribers, so inbound port forwarding will not work without a public IP.