Your Brain Weighs 3 Pounds—But Feels Heavier on Mondays

Your brain weighs about 3 pounds—roughly the same as a large cantaloupe or a small Chihuahua. Despite making up only 2% of your body weight, this wrinkly three-pounder burns through 20% of your daily calories just keeping you alive, thinking, and remembering where you put your keys.

The average adult brain weighs between 1,300 and 1,400 grams, though there's variation. Men's brains average around 1,370 grams while women's average about 1,200 grams—but before anyone gets smug, brain size has zero correlation with intelligence. Einstein's brain weighed 1,230 grams, below average for an adult male.

Shrinking Over Time

Your brain doesn't stay the same weight your whole life. It peaks in your early twenties, then gradually loses about 2-3 grams per year as you age. By the time you're elderly, you might have lost 10% of your brain weight—though you've hopefully gained wisdom to compensate.

Heaviest Organ? Not Even Close

Three pounds sounds substantial, but your brain isn't even the heaviest organ in your body. That honor goes to your skin (about 8 pounds) and liver (around 3.5 pounds). The brain wins on complexity, though, with 86 billion neurons firing signals across 100 trillion connections.

What Takes Up All That Weight?

• 60% fat - making it the fattiest organ in your body
• Water - about 73% water content
• Protein and carbohydrates - the remaining structure
• No pain receptors - you can't feel your brain itself

Those three pounds contain everything that makes you you—your memories, personality, ability to read this sentence, and that song stuck in your head. Not bad for something you could mail in a shoebox.

The Energy Hog

While your brain accounts for just 2% of your mass, it demands 20% of your oxygen and calories. When you're thinking hard—solving puzzles, learning new skills, or trying to understand cryptocurrency—that number can spike even higher. Your brain runs on about 12 watts of power, which is less than your refrigerator light but enough to keep 86 billion neurons humming along.

So next time someone says they're tired from "thinking too hard," they're not entirely wrong. That three-pound supercomputer between your ears is literally burning calories to figure things out.