What is 1 atomic mass unit equal to?

1 atomic mass unit (1 amu) is equal to 1/12th of the mass of a carbon-12 atom. In SI units, it is approximately 1.66 × 10⁻²⁷ kilograms.

The atomic mass unit is a standard unit used to express atomic and molecular masses. Since atoms are extremely small, their masses cannot be expressed in grams, so a relative unit (amu) is used.

Value of 1 amu

• 1 amu = 1/12 of carbon-12 atom
• 1 amu = 1.66 × 10⁻²⁷ kg
• 1 amu = 931 MeV/c² (in energy units)

Why Carbon-12?

Carbon-12 was chosen as the standard because it is stable, widely available, and convenient for calculations in chemistry and physics.

Applications

• Measuring atomic masses of elements.
• Comparing molecular masses in chemistry.
• Used in physics for nuclear and particle studies.

Example

Hydrogen atom has a mass of about 1 amu, while oxygen has about 16 amu. This shows oxygen is about 16 times heavier than hydrogen.