It's no secret that Mount Everest, the jewel in Nepal's Himalayan crown, is the world's premier mountain. It's one of those facts embedded in childhood, like knowing that Neil Armstrong was the first person to walk on the moon 

So, judging by different parameters — including tallest by altitude, tallest from base to top and tallest based on being the farthest point from Earth's center — what is the tallest mountain in the world? 

Researchers have measured Mount Everest many times over the past few decades, but the latest assessment, announced in November 2021, puts it at 29,031.69 feet (8,848.86 meters) above sea level, which is almost 5.5 miles (8.8 kilometers) tall. It's a pretty impressive height, but it does raise a question: Why do we use "above sea level" when determining the world's tallest peak?  

Elevation is now measured in relation to the mathematically defined geoid of the Earth," he said. The geoid is, according to the National Oceanic and Atmospheric Administration, "a model of global mean sea level that is used to measure precise surface elevations." This average is used to ascertain the height of mountains, a process that sometimes requires an aeroplane to fly "back and forth over a mountain in a series of parallel lines to measure how much gravity pulls down on its peak," according to GIM International. These measurements, in conjunction with GPS readings, provide incredibly accurate elevation readings. 

So, all mountains are measured from sea level, predominantly for convenience and consistency, but what if measurements were simply taken from base to peak? Would Everest still top the charts? 

The answer is a mountainous "no." That honor would go to Mauna Kea, an inactive volcano in Hawaii. Although its peak is 13,802 feet (4,205 m) above sea level — which is less than half the height of Everest, according to National Geographic — the majority of Mauna Kea is hidden below sea level. When measured from base to peak, Mauna Kea is 33,497 feet (10,211 m) tall, according to the United States Geological Survey, which puts it heads and shoulders above Mount Everest.

Should we, therefore, regard Mauna Kea as the tallest mountain on Earth?

It all depends on the perspective you take.

Mount Everest is the tallest mountain above sea level, while Mauna Kea can certainly claim to be the world's tallest mountain (when sea level isn't taken into account). It would be difficult to make a case for Chimborazo being the tallest, but "it's all a matter of perspective," Price admitted.

Regardless of the mountain you choose, its height will pale in comparison with Mars' Olympus Mons, the largest known volcano in the solar system. It has a height of around 16 miles (25 km), according to NASA, which is almost three times taller than Everest, and a base of 374 miles (601.9 km) in diameter, which is about the same distance separating San Francisco and Los Angeles (383.1 miles/616.5 km).