Elevation vs Altitude vs Height

This terminology article serves the disambiguation function — many readers come from different domains (hiking, aviation, surveying, programming) and assume their domain's usage is universal. It isn't. This article maps the terms across domains, explains why each domain has its conventions, and notes the practical implications.

Companion to /learn/vertical-datums-explained, /learn/mean-sea-level-explained, and /learn/the-geoid-explained.

The three terms in everyday speech

In casual English, elevation, altitude, and height are roughly synonymous: all mean “how far above something is” in the vertical direction. Without technical context they're interchangeable.

"The mountain's elevation is 8,000 ft."
"The mountain's altitude is 8,000 ft."
"The mountain's height is 8,000 ft."

All three are acceptable in everyday speech and convey the same information. But in technical contexts, each has distinct, sometimes contradictory meanings.

Elevation in surveying

In surveying and topographic mapping, elevation specifically means orthometric height above mean sea level:

• “Denver's elevation is 5,280 ft above MSL.” (Denver is “the Mile-High City.”)
• “The benchmark's elevation is 1,247 m.”
• “Mount Everest's elevation is 8,848.86 m.”

Surveyors and GIS practitioners use elevation for terrestrial features: ground level, peaks, valleys, survey benchmarks. They use height for structures or objects above the elevation: a building 50 m tall sits on a foundation at 1,000 m elevation; the top of the building is 1,050 m elevation.

The reference for elevation is typically:

• MSL (mean sea level) historically.
• Orthometric height (height above the geoid) in modern usage.
• National vertical datum (NAVD88 in US, ODN in UK, EVRF in Europe) for high-precision work.

See /learn/vertical-datums-explained for the datum framework and /learn/mean-sea-level-explained for how MSL is measured.

Altitude in aviation

Aviation has the most elaborate altitude terminology because pilots need to distinguish multiple aspects of “how high am I?” for safe and efficient flight.

The six commonly distinguished aviation altitudes:

Indicated altitude

What the altimeter reads. The altimeter is a barometer calibrated to convert atmospheric pressure into a height value. The conversion depends on the altimeter setting (the local sea-level pressure the pilot dials in).

Indicated altitude is what the pilot looks at most often. ATC instructions reference indicated altitude (“descend to 5,000 feet” means indicated altitude 5,000 ft).

True altitude

The actual height above mean sea level. Matches indicated altitude only when the altimeter setting matches the actual local atmospheric pressure. On non-standard days (warm, cold, high-pressure, low- pressure), true altitude differs from indicated.

The mnemonic: “True alt the chart, indicated alt the gauge.” Survey-quality terrain elevation on the chart is true; the altimeter shows indicated.

Absolute altitude (AGL)

Above Ground Level — height above the terrain directly below the aircraft. Varies with terrain: flying at constant indicated altitude over a mountain range, the AGL fluctuates as the terrain rises and falls.

AGL matters for terrain avoidance, especially for low-flying aircraft (helicopters, agricultural aircraft, military terrain-following missions). Radar altimeters measure AGL directly (vs barometric altimeters that measure indicated altitude).

Pressure altitude

Indicated altitude when the altimeter is set to the standard sea-level pressure: 29.92 inches of mercury (inHg) or 1013.25 hectopascals (hPa).

Pressure altitude is used:

• For all flight above 18,000 ft in the US (transition altitude). Above the transition, all aircraft use the same standard setting, ensuring vertical separation between aircraft.
• For aircraft performance calculations: engines and wings operate based on air pressure, not on actual height above sea level.
• For ICAO flight levels: “FL350” means 35,000 ft pressure altitude.

Density altitude

Pressure altitude corrected for non-standard temperature. The standard atmosphere assumes 15 °C at sea level, decreasing by 2 °C per 1,000 ft. Real days are hotter or colder than standard.

Hot days → higher density altitude (thinner air, worse engine and wing performance). Cold days → lower density altitude (denser air, better performance).

Why it matters: on a hot summer day at Denver airport (already at 5,280 ft MSL, pressure altitude might be 6,000 ft after the local altimeter setting, plus 30 °C → density altitude 9,000+ ft). An aircraft performs as if it's at 9,000 ft, even though the pilot is on the ground. Density altitude is the performance reality that the aircraft engine and wings actually respond to.

Pilots check density altitude before takeoff in hot or high-altitude conditions, particularly for small aircraft with marginal performance.

Geopotential altitude

Used in atmospheric science rather than aviation operations. Geopotential altitude accounts for the variation in gravitational acceleration with altitude — at higher altitudes, gravity is slightly weaker, so the same potential-energy difference corresponds to slightly more linear height.

For most aviation, geopotential and geometric altitudes are essentially identical at flight altitudes (< 60 km). For weather balloons, high-altitude research, and atmospheric models, geopotential altitude is the rigorous reference.

Altitude in geodesy

In modern geodesy, altitude sometimes refers to ellipsoidal height — height above the WGS 84 reference ellipsoid. This is the height GPS naturally produces.

• Ellipsoidal height (h): height above the WGS 84 ellipsoid. GPS gives this directly.
• Orthometric height (H): height above the geoid. What surveyors and topographic maps use.
• Geoid undulation (N): h = H + N. Ranges from -106 m to +85 m globally.

A GPS receiver displaying “altitude” may be showing either ellipsoidal or orthometric — depending on whether the receiver applies an internal geoid model.

For most consumer GPS devices (smartphones, hiking GPS), the displayed value is orthometric after applying an internal model (typically EGM96 or EGM2008). For surveying-grade GPS, the value is ellipsoidal unless explicitly converted.

Altitude in astronomy

A completely different meaning. In astronomy:

• Altitude is the angle of a celestial body above the horizon, in degrees.
• 0° = at the horizon.
• 90° = directly overhead (zenith).
• Negative = below the horizon.

Combined with azimuth (angle along the horizon from north), altitude specifies a celestial body's position in the local horizontal coordinate system.

This is the same usage as in /learn/celestial-navigation and /learn/the-sextant-explained: a sextant measures the “altitude” of the sun, meaning the angle above the horizon.

The astronomical altitude meaning has nothing to do with the aviation/geodetic linear-distance meaning. Both fields use the same word for different concepts; context distinguishes.

Height in everyday speech and engineering

Height is the most generic term:

• Building height: distance from ground to roof.
• Person's height: distance from feet to top of head.
• Tree height: distance from ground to top of canopy.
• Mountain height: from base to peak (note: this is prominence-like, not elevation).

In engineering, height is typically relative to a local reference rather than to MSL. A building's “height” is measured from its foundation or ground level, not from MSL.

In physics, height is vertical position difference in a gravitational field — used for potential energy calculations.

Mountain height: elevation vs prominence

Two distinct measures for mountains:

• Elevation (height of peak above MSL): the conventional “height” in atlases and encyclopedias. Mount Everest's elevation: 8,848.86 m.
• Prominence (height of peak above the lowest col separating it from the next higher peak): a measure of how isolated the peak is. Mount Everest's prominence: 8,848.86 m (it's the highest point on Earth, so its prominence equals its elevation).

The two values can differ enormously:

• Mauna Kea: elevation 4,207 m above sea level (lower than Everest), but base-to-peak is 10,210 m (much taller than Everest if measured from its ocean-floor base — sometimes claimed to be “the tallest mountain.”)
• Mount Damavand (Iran): elevation 5,610 m, prominence 4,667 m.
• Denali (Alaska): elevation 6,190 m, prominence 6,148 m (very high prominence because Denali rises from low-elevation surroundings).

For climbing rankings, prominence is often the preferred measure: Everest is the highest summit, but the “Seven Summits” mountaineering goal uses elevation. Sub-peaks that don't have significant prominence (Lhotse, Kangchenjunga's West Summit) aren't in the “Seven” even though they're among the highest points by elevation.

Linguistic origins

The terms came from different sources:

• Altitude: Latin altitudo, from altus “high.”
• Elevation: Latin elevare “to raise.”
• Height: Old English hīehthu, meaning “the highest part.”

English absorbed both Latin terms (altitude, elevation) and the Germanic one (height) over centuries. The distinctions in technical usage are 19th- and 20th-c. conventions rather than ancient distinctions.

Domain conventions summary

| Domain | Default term | Reference | | ------ | ------------ | --------- | | Surveying | Elevation | MSL (orthometric height above geoid) | | Topographic mapping | Elevation | MSL | | Hiking / outdoor recreation | Elevation | MSL | | Aviation | Altitude (multiple types) | Mostly pressure-based | | Atmospheric science | Geopotential altitude | Geopotential, varies with gravity | | Weather radiosondes | Geopotential height | Geopotential | | GPS surveying | Ellipsoidal height | WGS 84 ellipsoid | | GPS consumer (smartphone) | Orthometric height | Geoid (via internal model) | | Astronomy | Altitude | Local horizon (angular) | | Engineering / construction | Height | Local ground level | | Physics | Height | Local reference (potential energy) |

Cross-domain misunderstandings

The terminology overlap causes several common miscommunications:

Aviation engineer talking to GIS programmer: the engineer's “altitude” is pressure-based; the programmer's “elevation” is MSL-based. They differ by altimeter-setting effects; small but real.

Programmer using GPS API: API returns “altitude” — but which? Some APIs return ellipsoidal height; some apply a geoid model and return orthometric. The difference can be 100 m. Check the API documentation.

Astronomy app developer: “altitude” in the celestial-coordinate sense; nothing to do with linear height above sea level. Don't store as “meters above MSL.”

Weather data interpretation: pressure heights in weather products are geopotential, not geometric. For high-altitude work, they differ noticeably.

How to communicate clearly

Best practices for technical communication:

• Specify the reference: “1,247 m above MSL” rather than “1,247 m elevation.” “1,247 m above WGS 84 ellipsoid” vs “above geoid.”
• Use the domain's preferred term: in aviation conversations, “altitude”; in surveying, “elevation.”
• Document API conventions: when designing a programming interface that exposes height, specify the reference (ellipsoidal vs orthometric) and the vertical datum.
• Quote the source: “Everest is 8,848.86 m per the 2020 Nepal-China joint survey” tells the reader which value and what reference was used.

Common misconceptions

“Altitude and elevation are interchangeable.” In casual speech yes. In technical contexts, no. Aviation uses altitude with specific meanings; surveying uses elevation specifically.

“Pressure altitude is what the GPS shows.” No. GPS shows geometric height (either ellipsoidal or orthometric, depending on the device). Pressure altitude is from the altimeter (barometric), not the GPS.

“Density altitude is just pressure altitude.” No — density altitude is pressure altitude corrected for non-standard temperature. Hot days can have density altitude much higher than pressure altitude; cold days lower.

“GPS gives MSL elevation.” GPS gives ellipsoidal height. Conversion to MSL/orthometric requires a geoid model. Many consumer devices apply the model internally; surveying-grade devices may not.

“Mount Everest's height is its elevation.” Generally yes (8,848.86 m). Prominence is also 8,848.86 m for Everest because it's the highest point on Earth. For other peaks, elevation and prominence differ — Mauna Kea's elevation is 4,207 m but its base-to-peak is over 10,000 m.

“Altitude in astronomy is the same as in aviation.” Completely different. In astronomy, altitude is an angle above the horizon. In aviation, altitude is a linear distance. Don't confuse them.

“Sea level is constant everywhere.” No — MSL varies by location due to sea surface topography (±1 m globally). See /learn/mean-sea-level-explained.

“Orthometric height and elevation are exactly the same.” Approximately yes, but orthometric height refers specifically to the geoid; elevation is sometimes loosely “above MSL” which differs from the geoid by sea surface topography. For high precision, distinguish; for typical use, treat as synonymous.

“Building height is from MSL.” Usually from ground level, not from MSL. A 100 m building on land at 1,000 m elevation has a top elevation of 1,100 m MSL but its “height” is 100 m.

“Aviation pilots only care about indicated altitude.” Indicated is for navigation and ATC. Density altitude is for performance calculation. True altitude is for terrain clearance verification. AGL is for low-altitude operations. Each has a use; pilots check several.

“Geopotential and geometric altitude are the same.” Approximately at flight altitudes; diverge significantly at > 50 km. For satellites and atmospheric science, the distinction matters. For aviation, it's negligible.