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Ocean Sunfish Size: The Heaviest Bony Fish in the World

How big is a mola mola? Ocean sunfish size, weight and record holders – plus the giant sunfish that took the title of heaviest bony fish ever found.

By Strangest Animals · Updated 24 Oct 2026

This giant ocean sunfish seems almost as curious about the diver with the camera as the diver is about it!

The ocean sunfish, or mola mola, looks like a giant head that forgot to grow a body. It’s also enormous. Divers who meet one for the first time often describe it as swimming next to a floating dinner table. So how big do sunfish really get?

Sunfish size in numbers

Length: adults are usually about 6 ft (1.8 m) long, and big ones reach around 10 ft (3 m).
Height: measured from fin tip to fin tip, they can be taller than they are long, up to about 14 ft (4.2 m).
Weight: usually between about 550 and 2,200 lb (250 to 1,000 kg).

Sunfish vs. you

Height: a big sunfish standing on its tail fin would be more than twice as tall as an adult person.
Weight: a large one weighs about as much as a small car.
Brain: despite all that bulk, its brain is tiny, smaller than a walnut.

The heaviest bony fish in the world

For a long time, the ocean sunfish was called the heaviest bony fish in the world. Scientists now know the record actually belongs to its close relative, the giant sunfish (Mola alexandrini). In 2021, a dead giant sunfish found off the Azores weighed 2,744 kg, about 6,050 lb, the heaviest bony fish ever recorded.

The two species look very similar, which is why old records were often mixed up. Sharks and whales are heavier, but sharks have skeletons of cartilage, not bone, and whales are mammals.

The biggest fish with real bones isn’t a tuna or a marlin. It’s a giant, wobbly swimming head.

From a pinhead to a car

A newly hatched sunfish is about the size of a pinhead. An adult can be around 60 million times heavier, one of the biggest growth spurts of any animal with a backbone. A female can carry an estimated 300 million eggs at once, more than any other known vertebrate.

Strange but trueOne sunfish at the Monterey Bay Aquarium put on about 800 lb (365 kg) in just 15 months. It had to be moved out to sea because it was outgrowing its tank.

The sunfish that hid for centuries

In 2017, scientists described a brand-new sunfish species, the hoodwinker sunfish (Mola tecta). It had been hiding “in plain sight” in museum collections for centuries because people thought it was just an ocean sunfish.

Why is the sunfish so big?

Mostly because it eats a lot of jellyfish and other soft animals, which aren’t very nutritious, so it eats enormous amounts. Its size also helps it stay warm on deep, cold dives. Few predators can tackle an adult, although sea lions, orcas and large sharks sometimes do.

Want more record holders? See our Giants collection.