Airport Runways: What do those big numbers mean?

Airports · 5 min read · May 21, 2024

To the uninitiated, aviation and airport operations might look strange and confusing with many different signs, airport runways, designations, and markings. Airports are incomplete without these signs and numberings which are placed systematically at specific locations and are the basic points on which airports are built, operated, and functioned.

To the aviation industry, these letters, numbers, and markings make complete sense and are fundamentally significant in order to carry out airport operations safely. Runway markings and runway numbers are one of them.

A central view of a runway with a marking '15' at Rome Ciampino airport on a clear day in Italy.

What are the airport runaway numbers?

Airport runway designations are numbers based on the magnetic azimuth (compass bearing) in which a runway is oriented. These are painted in white on the end of the runway on both sides and are quite large in size.

How runways are numbered?

As there are 360 degrees on a compass, therefore runways are numbered between 01 and 36. This is done by dropping the last digit from the compass bearing or from the magnetic heading of the runway and rounding it to the nearest 10 degrees. This means a magnetic heading of 360 degrees for a runway would be painted on the runway as 36 and is pronounced individually as runway three six (Runway 36). These are simplified by the FAA to avoid any confusion and to allow pilots from anywhere in the world to quickly decipher the numbers, ensuring clear communications and safety.

As runway markings are based on the compass direction, 360 represents north (runway 36), 90 represents east (runway 09), 180 represents south (runway 18) and 270 represents west (runway 27). In short, the runway numbers mean headings.

These runway designations are mostly standardized throughout every major airport in the world. The opposite end of any given runway (180 degrees away) will be plus or minus 18 in the runway number, which is basically 180 degrees reciprocal of the given number (for example runway 08 in one direction and runway 26 in the other direction).

Airport runway numbers change from time to time. Due to changes in the earth’s molten iron core, the earth’s magnetic north pole is on the move which causes the numbers to change and the FAA rechecks them every five years. Such magnetic shifts are more frequent in airports at high latitudes that are closer to the poles.

In 2009, the Fairbanks International Airport in Alaska renamed runway 1L-19R to runway 2L-20R when there was enough shift in the magnetic north to mandate a change. The interval of change at this airport is roughly every 24 years.

Aircrafts parked by a runway with markings "yield" and "20 mph" at an airport in the mountains.

Parallel runways and designations

In the case of busy and large airports, especially an international airport, there can be more than one parallel runway to maintain an orderly flow of air traffic. With multiple airport runways, runway designation can take the form of a combination of numbers and letters.

Airports with two parallel runways going in the same direction are designated as the left or right runway with an L or R. For example, Runway 18 will be called 18L or 18R. This direction is relative to the direction the aircraft is facing. Some airports also have three parallel runways and in this case, the designation of C will be assigned to the runway in the center. For example Runway 18L, 18C, and 18R. In rare instances where four runways run in parallel, there is no fourth designation and instead, one number is shifted by 10 degrees. Such runways are separated by several hundred feet.

It is important to note the direction in which an aircraft will take off or land on a particular runway. Departing from Runway 18L means that you are heading South. However, on the same runway, if the aircraft was taking off in the opposite direction, it means that it was heading North at heading 360 degrees. (Heading 360 degrees is reciprocal or opposite of heading 180 degrees). This is why runways have two numbers at each end, where direction changes accordingly. Therefore, the complete runway number would be 18L-36R for one end and 18R-36L for the other end.

Practical application

An example of a busy airport is Boston, Massachusetts’ Logan International Airport which has two pairs of parallel runways, one numbered Runway 4L-22R and the other 4R-22L. Atlanta Airport is an exceptionally busy airport with five active runways. There is a runway 26L and 26R, a runway 27L and 27R, and a runway 28. Each of these runways has the same heading of  274.4 degrees magnetic but is given different runway designations with a shift of ten degrees, making a one-digit difference in the runway numbers.

Therefore, it is vital for the pilots, air traffic control, and other aviation personnel to be familiar and clear with the airport layout and regulations, especially the critical and busy areas including the runways and the taxiways. Without these rules and regulations, there would likely be chaos in the air and on the ground. Due to this, uniformity and similarity are adopted by all the airports worldwide to leave little room for confusion, misunderstandings, or mistakes, especially at critical times.

As the runway markings are always white in color, there are also visible signs on the ground at different positions and locations to indicate the runways including white text on a red background. On the other hand, taxiways are indicated by yellow letters on a black background, making the difference between them quite clear and understandable.

A single number is 63 feet tall by 20 feet wide in the US. This large size is very useful for situational awareness because on every take off the plane rolls over these numbers, giving a good reference for landing and a visual indicator confirming that the aircraft is lined up correctly on the assigned runway.

A bird's-eye view of the taxiway and the runway 27R at Hartsfield-Jackson Atlanta International Airport.

Effect of wind and its consideration

Winds play the most important part in considering the runway direction and orientation. When an airport is being designed, designers research the prevailing winds in order to locate the ideal orientation for the runway. Therefore, runways are not simply lined up at airports but are built and aligned to take advantage of prevailing winds to assist in takeoff and landing. These winds can shift direction and pattern and therefore many large airports have a wide range of runway configurations that can be used in either direction to accommodate these changes in seasonal wind directions. Although not all airports are large enough to accommodate this, runways running at different angles allow the pilot of an aircraft to align better with the wind.

Depending on these changes in the wind, runways are used in either direction as aircraft depart and land into the wind in order to maximize the lift when taking off and drag while landing, and to minimize the ground roll.  Depending on the actual conditions prevailing at the time, air traffic control can instruct pilots to use either direction for the conduction of safe flight operations.

Therefore, selecting the ideal location of the runway is a very crucial part of airport planning and building.

However, it is important to note that in the case of Naval aircraft carriers, the scenario is not the same. There are no runway designators painted on the flight deck of these carriers as the wind direction is constantly changing and altering in the open seas. The fundamental role of wind orientation in terms of take-off and landing remains the same and therefore, the ship is turned into the wind.


Regulators, operators, and other organizational bodies throughout the world are in a constant search of new and modern solutions to make aviation more safe, reliable, and efficient in order to facilitate both the crew and the passengers. Making runway operations more smooth, quick, and orderly is a part of such developments.

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Aeroclass Team
A team of professionals with a deep passion for the aviation industry bringing you the newest and the most striking industry-related news and content.

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