What is Atomic mass units (amu)?

Atomic mass units (amu) are tiny weights used to measure how heavy atoms are, like a super-light scale for teeny-tiny things you can’t see.

Imagine you have two jellybeans: one is a regular red jellybean, and the other is a giant chocolate-covered jellybean. The red one feels light, and the big one feels heavier. Now, if we had a scale that could measure how much each jellybean weighs, but only in the tiniest bits, that’s like using atomic mass units.

Atoms are like those jellybeans, super small, and they have different weights. Scientists use amu to tell them apart, just like you might say one jellybean is lighter than another.

For example:

• A hydrogen atom weighs about 1 amu, it’s like the red jellybean.
• A carbon atom weighs about 12 amu, that’s more like the big chocolate-covered jellybean.

So when scientists look at atoms, they use amu to count how heavy they are, just like you might count jellybeans by weight.