Altitude means height above the ground or above the sea level. Common uses include aviation (flying, parachuting, gliding), and geography/surveying. In geometry it is also used as the height of the object itself. Generally, altitude is the distance one thing is above another thing. This is in the vertical or "up" direction. For the height of the ground (such as for hills and mountains), the word elevation is also used and might be a better choice. (Mountain climbers usually use the word altitude, especially when talking about how it affects the body). Buildings and other things on the ground usually just use the word height.

Vertical distance measurements in the "down" direction are commonly referred to as depth.

Altitude in aviation and in spaceflight

Vertical Distance Comparison

In aviation, the altitude can be measured and shown in several different ways. The height is either from the average sea level (also called Mean Sea Level or MSL), or from the ground (also called Above Ground Level, or AGL).

Airplanes can find their altitude by using air pressure. The air gets thinner the higher it is (and it has less pressure, because there's less air pushing down on it from above). This pressure can be measured and this can be converted into a height above sea level. The instrument for measuring altitude is the altimeter (from altitude and meter). The common pressure altimeter is a type of barometer with a dial showing distance (feet or metres) instead of atmospheric pressure.

There are several types of aviation altitude.

In simple terms, these types of altitude can be explained as ways of measuring the altitude:

  • Indicated altitude -- What the altimeter indicates (shows) for the height above sea level. It is usually pretty good, but can be fooled a bit sometimes, it needs to be adjusted to use the local barometric pressure.
  • True altitude -- Altitude as the distance above sea level.
  • Absolute altitude -- Altitude as the distance above the terrain (the ground) directly below it (Above Ground Level).
  • Height -- Altitude in terms of the distance above some point. This can also be called the terrain elevation. Radio altimeters measure this height.
  • Pressure altitude -- Altitude measured using air pressure. The air pressure at sea level is normally 1013.25 millibars or 29.92" Hg, when the air temperature is 15 °C (59 °F). Pressure altitude and indicated altitude are the same when the altimeter is adjusted to use this standard level.
  • Density altitude -- Altitude measured using the density of the air. This depends on atmospheric conditions (mainly heat and humidity). There is a International Standard Atmosphere chart that converts density to altitude.

The density of the air also affects how well an aircraft works. Density altitude is affected by barometric pressure, humidity and temperature. On a very hot day, density altitude at an airport (especially one at a high elevation) may be so high that aircraft can not take-off. This most often affects helicopters or an aircraft that is carrying a large amount of cargo.

Other Languages
aragonés: Altaria
asturianu: Altitú
Bân-lâm-gú: Hái-poa̍t
català: Altitud
Deutsch: Flughöhe
ދިވެހިބަސް: އުސްމިން
English: Altitude
español: Altitud
estremeñu: Altol
euskara: Altitude
français: Altitude
furlan: Altitudin
Gàidhlig: Àirde
galego: Altitude
客家語/Hak-kâ-ngî: Hói-pha̍t
한국어: 고도 (높이)
Bahasa Indonesia: Altitudo
italiano: Altitudine
қазақша: Альтитуда
lietuvių: Altitudė
Ligure: Altitùdine
Limburgs: Huuegdje
lumbaart: Oltitüden
മലയാളം: ഉയരം
Bahasa Melayu: Altitud
Nederlands: Hoogte
日本語: 高度
occitan: Altitud
português: Altitude
română: Altitudine
Scots: Altitude
sicilianu: Altitùddini
slovenčina: Nadmorská výška
slovenščina: Nadmorska višina
српски / srpski: Апсолутна висина
srpskohrvatski / српскохрватски: Апсолутна висина
suomi: Altitudi
svenska: Altitud
Tagalog: Altitud
Türkçe: İrtifâ
اردو: ارتفاع
vèneto: Altitudine
Tiếng Việt: Cao độ
文言: 海拔
West-Vlams: Oogte
Winaray: Altitud
吴语: 海拔
粵語: 海拔
中文: 海拔