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To compare mountain heights on Mars and Earth, first check what each height is measured from. Earth elevations are commonly given above sea level; Mars has no ocean sea level, and its topography may be referenced to an equipotential surface called the areoid. A summit’s elevation above a planetary reference surface is also a different measurement from how far the mountain rises above its local surroundings.
Why the measurement baseline matters
A height is meaningful only when its reference point is clear. On Earth, elevations are commonly reported relative to sea level. NASA’s Mars Global Surveyor Laser Altimeter dataset documentation describes Martian topography as referenced to an equipotential surface called the areoid, rather than Earth’s customary sea-level reference. The areoid is a reference surface, not an ocean or literal Martian sea level. NASA Planetary Data System dataset description
There is a second distinction: a summit’s elevation above a planet-wide datum is not necessarily the same as the mountain’s local relief—the rise from a selected base to its summit. That difference matters especially for broad volcanoes, where choosing the boundary between the mountain and surrounding terrain affects the result.
What NASA’s published figures say
NASA sources give several useful figures, but they describe different comparisons. They should be attributed to their sources rather than averaged or treated as interchangeable measurements.
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| Mountain or comparison | Published figure | Measurement context |
|---|---|---|
| Olympus Mons | More than 25 miles (more than 132,000 feet, or 40 km) | NASA Science describes this as base to summit. NASA Science, “Mars: Facts” |
| Mount Everest | 29,029 feet (8,848 m) | NASA Science lists this as Everest’s height above Earth’s surface. NASA Science, “Mars: Facts” |
| Olympus Mons and Everest | Over 27 km (~90,000 ft) and about 9 km (~29,000 ft), respectively; the poster says Olympus Mons is about three times as tall | NASA/JPL’s educational poster presents these figures as its comparison; they are not a universal ratio for every height definition. NASA/JPL, “How High Are the Mountains?” |
| Olympus Mons and Mauna Kea | About 23 km and about 10 km, respectively | NASA Goddard’s educational comparison gives Mauna Kea’s height measured from the ocean floor; its description does not establish that the Olympus Mons figure uses the same local-base definition as every other source. NASA Goddard Space Flight Center, “Earth-Mars Volcano Comparisons: Elevation Color-Mapped Mars” |
Is Olympus Mons really three times taller than Everest?
That is a fair shorthand for the comparison in NASA/JPL’s educational poster, which gives Olympus Mons as over 27 km and Everest as about 9 km. It is not safe to state “exactly three times” as a definition-independent fact. NASA Science’s current Mars facts page instead describes Olympus Mons as more than 25 miles (40 km) from base to summit and gives Everest as 29,029 feet (8,848 m) above Earth’s surface. The sources use distinct descriptions and comparison setups, so their figures do not produce one universally standardized ratio.
How to make a fair comparison
- Write down the reference surface. For each elevation, identify whether it is measured above Earth’s sea-level reference, Mars’s areoid, or another stated datum.
- Check whether the number is elevation or relief. A summit’s height above a datum and its rise from the mountain’s local base answer different questions.
- Use compatible definitions for both mountains. For a direct ratio, compare measurements made with the same type of baseline and clearly defined local bases. If sources use different definitions, report their numbers separately and explain the mismatch.
NASA’s own Mount Sharp comparison illustrates the issue: it says Mount Sharp’s elevation is relative to the floor of Gale Crater, while Mount Rainier, Mount McKinley, and Mount Everest are shown relative to Earth’s sea level. The graphic is a visual comparison, but those stated baselines differ. NASA/JPL-Caltech/MSSS, “Mount Sharp Compared to Earth’s Tallest Mountains”
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What to say when quoting a mountain’s height
Include the number, its baseline, and the source’s definition in the same sentence. For example: “NASA Science describes Olympus Mons as more than 40 km from base to summit.” That phrasing preserves the measurement NASA actually states without implying that it is a datum elevation or that every source uses the same base.
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A single definitive ratio requires measurements for both mountains made under one consistent definition. The NASA educational materials cited here do not provide a standardized table of local-base heights for all the named mountains, so avoid creating a more precise comparison by combining figures from different sources.
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