How Big Are Blue Whales Really? (And More Importantly: Why?)

If you're small enough, you could feasibly fit inside a blue whale's heart – though we don't recommend it.


Dr. Katie Spalding

Katie has a PhD in maths, specializing in the intersection of dynamical systems and number theory.

Freelance Writer

A blue whale seen from above. It big
Almost too big to fit into a 3200x1800 header image. Image Credit: Chase Dekker/Shutterstock

Regardless of all the terrible things going on in the world today, you have to admit, we’ve got things pretty lucky sometimes. For example, we get to live at the same time as the biggest animal ever known to exist on Earth: the blue whale. 

“When you are in a small boat on the ocean and a 25-meter-long blue whale surfaces 10 meters away from you, you gasp and you shed tears,” Richard Sabin, Principal Curator of Mammals at the Natural History Museum, London, told IFLScience. 


“They are breathtakingly beautiful,” he said. 

How big is a blue whale?

So what makes blue whales so special? Well, let’s start with the obvious: they’re utterly massive.

“We live in a time of giants,” said Jeremy Goldbogen, co-director of the Hopkins Marine Station and Associate Professor of Biology at Stanford University, in a statement. “Baleen whales have never been this big, ever.”

Even among baleen whales – whales who use large plates of bristly keratin to filter their prey out of the sea, rather than using teeth to chomp and chew it – the blue whale stands out. They can reach lengths of 33 meters (108 feet), making them the only living beings on the planet able to touch two consecutive baseball bases at the same time.


To put it another way, if a blue whale could stand upright on its tail fins – which it can’t, because it’s so large that it would almost certainly be crushed under its own mass on land – it would be about two and a half times the height of a brachiosaurus, six times the height of a giraffe, and fifteen times the height of Shaquille O'Neal.

Hope, the blue whale skeleton suspended above the entrance of London's Natural History Museum.
Hope, the blue whale skeleton suspended above the entrance of London's Natural History Museum. Image credit: Tom Eversley/ 

Weight-wise, they’re even more impressive. The second largest whales in the ocean are fin whales, and they can actually get pretty close to a blue in terms of length: they can grow up to 26 meters (85 feet) from nose to tail, making them more or less the “average US citizen” to their larger, bluer cousins’ Shaq. 

When you compare their weights, the size difference is way more obvious: a fin whale can weigh up to about 73 tonnes (80 tons), while a blue whale tops out at about 200 tonnes (220 tons) – almost three times as heavy.

How big is a blue whale’s brain?

All that bulk needs some mega-sized muscles and organs to get it moving. 


Let’s start with the brain. Almost immediately, we find a surprise: blue whales, gigantic as they are, do not in fact have the biggest brain on the planet.

Don’t look so cocky though – neither do we. Nowhere near. “We humans pride ourselves on our big brains,” wrote neuroscientist R. Douglas Fields in a blog post for Scientific American back in 2008. “The fact is, people do not have the largest brains on the planet, either in absolute size or in proportion to body size. Whales, not people, have the biggest brains of any animal on earth.” 

The creature with the largest brain is in fact the sperm whale – the largest of the toothed whales, made famous by the titular character in Moby Dick. Their brains are about 8,000 cubic centimeters – a cool six times larger than the one nestled inside your cranium right now, or “equivalent to the difference in engine displacement … of a 1960s VW beetle compared with two and a half Formula One race cars,” Fields explained.

A blue whale’s brain is a little smaller, at around seven kilograms (15 pounds) to the sperm whales’ nine kilograms (20 pounds). However, because they’re just so much bigger than other animals, those few kilos make a big difference overall. When you measure the encephalization quotient, or EQ, of both animals – a measurement of brain size that accounts for body size – the sperm whale tops out at around 1.28, while its gigantic blue cousin scores a comparatively puny 0.19.


A blue whale’s dachshund-sized brain isn’t the coolest thing about its titanic neurology. “One of the most interesting things to me about the brains of cetaceans is how big some of their neurons need to be in order to move information from their bodies to their brains and back,” wrote cognitive and computational neuroscientist Bradley Voytek for Nature Scitable.

“The largest blue whales are around 30 m long. This would suggest a DRG [dorsal root ganglion] axon of at least 25 m, or 75 feet, long,” he explained.

”This means that if I were to flick a whale's tail (as one might do), it could take anywhere from a third of a second (a long time in brain time!) to more than SIX SECONDS to reach the whales’ ‘conscious’ perception.”

How big is a blue whale’s heart?

Put it this way: if you’re a little on the short side, you could probably fit fairly comfortably inside a blue whale’s heart. It’s around 1.5 by 1.2 meters – that’s about five feet by four – and at 23 cm (9 inches) in diameter, the aorta is so wide you could shove a toddler inside it if the fancy took you.


The heart weighs up to 200 kilograms (440 pounds), and is around the size of “a small golf cart or circus bumper car for two,” according to Jacqueline Miller, a mammalogy technician at the Royal Ontario Museum. She should know: she led the preservation of a blue whale’s heart back in 2015 – a project which took many months thanks to the organ’s incredible size.

Not only is it large, but it’s incredibly powerful, pumping out around 220 liters (58 gallons) of blood per beat. That’s about two whole baths’ worth of liquid, all rushing out at once. This is somewhat made up for by the fact that a blue whale’s heart rate can be as low as two beats per minute (suck it, Usain Bolt).

That is remarkable, even to people who are used to blue whales’ weirdness. In 2019, a team of scientists from Stanford University became the first people ever to get a recording of a blue whale’s heartbeat, and they discovered a highly variable heart rate: as low as two beats per minute at the bottom of a dive, and as high as 37 bpm when the whale came to the surface for air. 

Both of those were surprising, but for different reasons. Based on their size, and going by the usual patterns of mammal bodies, the cerulean cetaceans should have a resting heart rate of around 11 bpm – much higher than their lowest rate, and much lower than their highest. But it turns out whales – as well as some other marine animals, like seals – have something smarter going on: they have a peculiarly stretchy aortic arch.


The aortic arch is the part of the heart that moves blood out to the body, and in humans it’s a pretty simple open-and-close valve. In whales, though, its elasticity means that it can continue contracting, and therefore pumping blood, in between heartbeats – and that’s how the colossal critters can survive on just two beats per minute.

And what about the speedier, surface-level heart rate? Well, that might be even more interesting.

Why are blue whales so big?

At 37 beats per minute, a blue whale’s heart is “beating as hard as it can possibly go,” Goldbogen, who headed the whale-recording project, told The Atlantic. “This was routine foraging behavior. They do this all day long.”

Which presents an intriguing possibility: could anything larger than a blue whale exist? Goldbogen suspects not: “they’re approaching their physical limits,” he said.


Put simply: when a blue whale dives down to feed, their heart rate drops, and they accrue an oxygen debt. To make up for that debt, when they come to the surface, their heart rate speeds up – think about how fast your own heart beats after you hold your breath too long, and you get the general idea. 

However, an even bigger animal’s heart wouldn’t be able to beat fast enough to make up for this deprivation, Goldbogen suggested. That would make diving for krill impossible – and without all that krill, this hypothetical über-whale would simply not be getting enough calories to survive.

“Of all present-day rorquals [the largest group of baleen whales], blue whales are arguably the most specialized. They eat krill and only krill, with very few exceptions,” wrote Eric M Keen in an article for Scientific American in 2020.

“To compete for krill, they have evolved for long-distance efficiency at the cost of maneuverability,” he explained. “Bigness is key to the blue whale’s diet, but bigness also adds to the whale’s overall energy budget … [the] blue whale has become trapped within a tautological circle of specialization: it needs to be big enough in order to eat enough to be big.”


Every time a blue whale swallows a mouthful of krill – which, we should remind you, are basically tiny floating bugs – it ingests around half a million calories. Of course, one bite is hardly enough for a meal, and a blue whale might eat 100 times that amount in one day.

“[They eat] somewhere in the range of 20 to 50 million calories,” Matthew Savoca told NPR. He’s a researcher at Stanford University, and lead author of a recent study that revealed just how much the animals eat – which turned out to be quite a bit more than scientists realized. 

“That is about 70- to 80-thousand Big Macs. Probably decades of our eating is one day for them,” he added. “It's pretty remarkable.”

That may be very good news – for krill, believe it or not. As science tells us, what goes in must come out, and more whale poop means more nutrients in the water. More nutrients in the water means more phytoplankton, and more phytoplankton means more tasty snacks for the krill.


“Whales are acting as mobile krill processing plants,” Savoca said in a statement accompanying the study. “These are animals the size of a Boeing 737, eating and pooping far from land in a system that is iron-limited in many places. These whales were seeding productivity out in the open Southern Ocean and there was very little to recycle this fertilizer once whales were gone.”

A blue whale pooping. Seen from above.
In case you've ever wondered what a whale pooping looks like. Just think of it as the Miracle-Gro of the seas. Image Credit: Elliott Hazen under NOAA/NMFS permit 16111

More phytoplankton also means more oxygen on the planet. The tiny organisms do more than simply underpinning every marine food chain – they also produce about as much oxygen as all the land plants combined, and play a vital part in the natural carbon cycle. That’s right: even as we drive them closer into extinction, blue whales are doing their part in the fight against global warming. By pooping.

“The contribution of whales to global productivity and carbon removal was [once] probably on par with the forest ecosystems of entire continents, in terms of scale,” said Nicholas Pyenson, curator of fossil marine mammals at the Smithsonian's National Museum of Natural History and co-author of the study. 

“That system is still there,” he added. “Helping whales recover could restore lost ecosystem functioning and provide a natural climate solution.”


  • tag
  • ocean,

  • animals,

  • whales,

  • cetaceans,

  • blue whales,

  • Marine biology