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Many different units can be used to designate the same things.

Degrees Celsius va Fahrenheit Altitude in feets or meters, ... Sometime different units measure the same thing but have different semantics or measure very similar things: Speed can be measured in Km/h or Mach number. Fuel can be measured in Kg or liters.

Some units can be also displayed relative to some other ones (ex we have n min of fuel left)...

What units are typically used in aircraft nowadays.

I'm particularly interested in:

  • Speeds
  • Pressure
  • Altitude
  • Distance
  • Weight
  • Volume
  • Position

Let's restrict the question to units displayed in the cockpit, and to Airbus or Boeing non military airplanes.

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marked as duplicate by fooot, Pondlife, SMS von der Tann, TomMcW, Simon Aug 9 '16 at 20:13

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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Airspeed, ground speed
Primary unit: km/h. Non-SI unit: knot.
In practise, knot is the main unit. At high levels, the Mach number is used, which is a measurement of speed relative to the local speed of sound.

Pressure
Pascal. Hectopascal is used for altimeter settings. In the USA they use inches of mercury.

Altitude
Primary unit: metres. Non-SI unit: feet.
In practise, feet is the main unit. Whether you say altitude or flight level depends on your reference air pressure.

Distance
Long: nautical mile. Short: metres. Vertical: foot.

Mass
Kilograms.

Volume
Litre or cubic metre.

Position
Latitude and longitude based on WGS84.

The above is according to ICAO Annex 5, which means that it is true for more or less all of the world. A few places prefer to deviate from the standard units, such as the USA, which uses a slightly different system.

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    $\begingroup$ What do you mean by "primary unit"? And why do you say "Non-SI" unit? Is it meant to be the opposite? If so, why don't you write that? Is it written like that in the Annex 5? $\endgroup$ – Mayou36 Aug 9 '16 at 18:56
  • $\begingroup$ Yes, that is how it is written in annex 5. $\endgroup$ – J. Hougaard Aug 9 '16 at 19:32
  • $\begingroup$ So what is the unit used to report fuel quantities ? Volume or Mass ? $\endgroup$ – Antzi Aug 10 '16 at 1:52
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    $\begingroup$ @Antzi Typically mass. Kilograms or tonnes. $\endgroup$ – J. Hougaard Aug 10 '16 at 6:52
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These units are either the common ones in the cockpit or what ATC (under the FAA) expects reporting in. Europe may report differently, but I consider the US in the "west" if you further specify where you are asking about the answer may change.

Speeds: Knots or Miles Per Hour, depends on the aircraft and the ASI installed. Some jets also use mach number.

Pressure: Inches of Mercury usually you can find this in the local ATIS. ATC (if you are entering a controlled area) will give you the altimeter setting using these units. For example you may hear "123AB Cleared to the field, Altimeter 29.91" when getting a Class C clearance

Altitude: Feet (usually 100's). When above 18,000 its usually referenced as a Flight Level. ATC expects reports in Feet when announcing altitude.

Distance: Nautical Miles or Statute Miles

Weight: Pounds

Volume: US Gallons (note this is different from an imperial gallon) for fuel or pounds, depends.

Position: "X miles north of Y Location" (or something similar). GPS locations can be used. When flying IFR or on airway a location identifier may be used.

With modern glass cockpits many of these units may be configurable. These units better reflect the older standard gauges used in the US many of which may still be in service.

This FAA handbook outlines instrument layout and the like, you may want to take a look at it for deeper specs but the units included in it are listed above.

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  • $\begingroup$ en.wikipedia.org/wiki/Western_world $\endgroup$ – J. Hougaard Aug 9 '16 at 18:05
  • $\begingroup$ I guess it really depends where you are standing, anything is to the west of anything else if you are willing to travel far enough.... $\endgroup$ – Dave Aug 9 '16 at 18:22
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    $\begingroup$ This is very US-centric. In other parts of the world, pressure is measured in hPa, weight in kg or tons, volume in litres. In some countries, altitude is metric, too. And even the distance is easier to find in kilometres than in statue miles. (We are still talking about aviation). $\endgroup$ – Zeus Aug 10 '16 at 3:35
  • $\begingroup$ I am aware that it is, however I fly in the US and these are the units I use. I was sure to be clear that I was answering for the FAA. I don't know what is used elsewhere as I don't fly out of the country yet. I did not want to answer something incorrectly about the units used in other parts of the world due to my lack of experience. $\endgroup$ – Dave Aug 10 '16 at 12:37

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