Earth's Tallest Mountain Depends on How You Measure It

Ask someone to name the world's tallest mountain, and the answer comes back instantly: Mount Everest. The Nepalese peak, standing 8,848.86 metres above sea level, has held that place in the popular imagination since Edmund Hillary and Tenzing Norgay reached its summit on May 29, 1953. But the question itself contains a trap. The moment you ask how to measure tallness, the answer fractures into three competing claims, each defensible, each true in its own way.

The confusion begins with a simple distinction that most people never consider. Everest is indeed the highest mountain above sea level—the peak that rises farthest from the ocean's surface. But height and tallness are not the same thing. If you measure from base to summit, from the mountain's lowest point to its highest, a different champion emerges: Mauna Kea in Hawaii, a long-dormant volcano that reaches a total of 10,205 metres. That makes it approximately 1.4 kilometres taller than Everest, a gap so substantial that it reshapes the entire conversation.

The catch is that most of Mauna Kea exists underwater. Of its 10,205-metre total height, only 4,205 metres rise above the Pacific Ocean. The remaining 6,000 metres sit submerged, invisible to anyone standing on the island's slopes. This hidden bulk is what gives Mauna Kea its true stature. The mountain's name translates to 'White Mountain,' a reference to the snow that frequently caps its visible peak, but the real story lies beneath the waves. The United States Geological Survey notes that despite being dormant for roughly 4,500 years, Mauna Kea is likely to erupt again—though there is little immediate cause for alarm. The sensitive astronomical telescopes that make the summit home to Earth's largest observatory would detect even minute ground tilts that might signal an impending eruption.

Hawaii holds a second claim to the title as well. Mauna Loa, another massive volcano on the islands, measures 9.17 kilometres from base to summit, with 5 kilometres of that height submerged. By the same base-to-peak measurement standard, it ranks as the second-tallest mountain on Earth, again surpassing Everest.

But there is a third contender, one that depends on yet another way of thinking about what 'tallest' means. Mount Chimborazo in Ecuador's Andes stands only 6,310 metres above sea level—substantially lower than Everest by that measure. Yet Chimborazo holds a distinction that no other mountain can claim: it is the peak closest to the sun. This oddity exists because Earth is not a perfect sphere. The planet bulges at the equator and flattens slightly at the poles, a shape called an oblate spheroid. Chimborazo sits just one degree south of the equator, closer to that bulge than any other mountain on the planet. If you were to measure from Earth's centre outward, Chimborazo's summit would be the farthest point on the planet's surface from that centre—making it, by that measure, the tallest mountain in the world.

In practice, the competition narrows to two. Everest retains the crown for highest above sea level, the measurement most people use and understand. Mauna Kea claims the title for greatest total height, base to summit. The latter achievement was only recently confirmed. In February 2021, American adventurer and retired Navy officer Victor Vescovo and Hawaiian marine scientist Dr Clifford Kapono became the first to complete a full ascent from Mauna Kea's base to its summit. They used a two-person submersible called the Limiting Factor to traverse the underwater portion, then rowed for five-plus hours in a three-person outrigger canoe toward Big Island. Over three days, they cycled, hiked, and skied to reach the summit, setting a Guinness World Record in the process. It was a feat that required not mountaineering alone but oceanography, paddling, and endurance across multiple disciplines—a fitting accomplishment for a mountain that exists in two worlds at once.