The answer may surprise you.
If you think the biggest mountain in the world is pretty obvious (a little hill known as Mount Everest), you may be surprised to learn the subject is a point of disagreement. As many as three mountains could take the title as the world's tallest mountain, though it all depends on your point of reference. Whether you measure from the base of a mountain to its summit, a mountain's distance from the center of the Earth, or its elevation above sea level can be the difference between Everest being the world's biggest mountain or just one of the highest peaks.
Mount Everest, in Nepal, is perhaps the most well-known contender—local officials have even announced plans to ban rookie climbers—and it's the tallest mountain on earth from sea level to peak. The storied mountain stands 29,035 feet above sea level and indisputably reaches the highest altitude.
But here’s where things get complicated. Mauna Kea, a dormant volcano on Hawaii's Big Island, extends deep beneath the Pacific Ocean. Measuring from its base to its peak, Mauna Kea reaches a staggering 33,947 feet. While you can only achieve an elevation of 13,796 feet above sea level by driving or hiking, this Hawaiian giant is nearly a mile taller than Everest.
It gets even more confusing when we consider Chimborazo, in Ecuador. Chimborazo’s summit is at 20,703 feet, which is clearly shorter than Mount Everest. Earth isn't a perfect sphere, however, and because Chimborazo is so close to the equator, this mountain rises from nearly the widest stretch of our planet. Technically speaking, Chimborazo is the highest mountain above the center of the Earth—no less than 1.2 miles farther away from Earth's core than Mount Everest.
So what really is the biggest mountain in the world? It turns out that, like everything else, it all hinges on perspective. And if you want to conquer the world's highest, tallest, all-around biggest mountain, you may want to summit all three. Just to be sure.