Portland International Airport, in Portland, United States.

What is the difference between PDX and KPDX?

PDX is the IATA code, used commercially — tickets, timetables, luggage tags. KPDX is the ICAO code, used operationally by pilots and air traffic control, and assigned geographically by region.

What airport is PDX?

PDX is

Portland International Airport

Portland, United States

Why the code is PDX

PD for Portland, plus the same meaningless X that LAX and PHX carry.

The airport authority or a contemporaneous record states this directly.

The airport

IATA code: PDX
ICAO code: KPDX
Airport: Portland International Airport
City: Portland, United States
Code origin: Documented

The X is filler from the 1930s expansion of two-letter weather-station codes to three letters. PDX has become a general shorthand for the city itself in a way few airport codes manage, appearing on local business names that have nothing to do with aviation.

The other code, KPDX

Every airport has two codes. The three-letter IATA code, PDX, is the one on your boarding pass and your luggage tag, and it is assigned for commercial use. The four-letter ICAO code, KPDX, is the one pilots and controllers use, and it is assigned geographically: the first letter or two identify the region, so every airport in the same part of the world shares a prefix. That is why KPDX looks nothing like PDX.

Common questions

What airport is PDX?: Portland International Airport, in Portland, United States.
Why is Portland's airport called PDX?: PD for Portland, plus the same meaningless X that LAX and PHX carry.
What is the difference between PDX and KPDX?: PDX is the IATA code, used commercially — tickets, timetables, luggage tags. KPDX is the ICAO code, used operationally by pilots and air traffic control, and assigned geographically by region.

United States Capital, area, population and currency
The flag of United States Colours, symbols and lookalikes
Airport codes in United States 32 here
What airport is JFK? John F. Kennedy International Airport, New York
What airport is LAX? Los Angeles International Airport, Los Angeles
What airport is ORD? O'Hare International Airport, Chicago
What airport is ATL? Hartsfield-Jackson Atlanta International Airport, Atlanta
What airport is MCO? Orlando International Airport, Orlando
What airport is DFW? Dallas/Fort Worth International Airport, Dallas
What airport is EWR? Newark Liberty International Airport, Newark
What airport is SFO? San Francisco International Airport, San Francisco

Sources

OurAirports — OurAirports (Public domain)

How these figures are compiled and checked