All things · Inside the Nucleus

Helium nucleus: how big is it?

Helium nucleus is about 3.4 fm. In everyday terms, that is ≈ 31,200 times smaller than a hydrogen atom.

Size

3.4 fm

In metres

3.40 × 10⁻¹⁵ m

Everyday comparison

≈ 31,200 times smaller than a hydrogen atom

Chapter

Inside the Nucleus

Did you know?

Two protons and two neutrons. Most of the helium in the universe was forged in the first few minutes after the Big Bang.

How it compares

• About 2× bigger than Proton (1.7 fm).
• About 4.4× smaller than Uranium nucleus (15 fm).

Other things of a similar size

• Quark (upper limit) 1.0 × 10⁻¹⁸ m
• Proton 1.7 fm
• Uranium nucleus 15 fm
• Hydrogen atom 106 pm
• Water molecule 275 pm
• Gold atom 288 pm

Sizes are rounded, typical values drawn from standard reference sources, including NIST/CODATA physical constants and NASA's planetary fact sheets. Real objects vary; see About for how sizes are chosen.