Skip to main content

Atomic Mass Units to Kilograms Converter
↔ Convert kg to amu instead

Common Conversions

amu kg
1 1.66054e-27
2 3.32108e-27
4 6.64216e-27
12 1.99265e-26
16 2.65686e-26
28 4.64951e-26
32 5.31373e-26
56 9.29902e-26
100 1.66054e-25
200 3.32108e-25
1000 1.66054e-24
10000 1.66054e-23

Why this conversion matters in chemistry

De Broglie wavelength calculations hits this regularly. A neutron at thermal energy (kT at 300 K, about 25 meV) carries 1.008 u of mass — 1.675 × 10⁻²⁷ kg — and lands at a wavelength of about 1.8 Å, the right scale to diffract off atomic spacings in a crystal. The ratio of 1.66054 × 10⁻²⁷ kg per u was a measured constant before 2019; the SI redefinition that fixed Avogadro's number at exactly 6.02214076 × 10²³ /mol made the equality exact. It comes up when atomic-scale physics has to come out in SI kilograms.

Formula

kg = amu × 1.66054 × 10⁻²⁷

Worked Examples

1 amu = 1.66054×10⁻²⁷ kg

The conversion anchor — one atomic mass unit in SI kilograms.

12 amu = 1.99265×10⁻²⁶ kg

One carbon-12 atom — the calibration anchor for the entire u scale.

6.022×10²³ amu = 0.001 kg

Avogadro's number of u — exactly one gram, by construction of the mole.

16 amu = 2.65686×10⁻²⁶ kg

One oxygen-16 atom — useful for any per-atom mass calculation in SI units.

Frequently Asked Questions

How do I convert amu to kilograms?
Multiply by 1.66054 × 10⁻²⁷. So 12 amu becomes 1.99265 × 10⁻²⁶ kg — one carbon-12 atom in SI units. The factor is exact through the 2019 SI redefinition that fixed Avogadro's number.
Where does the factor come from?
1 u = 1/Nₐ grams, with Nₐ = 6.02214076 × 10²³ /mol. So 1 u = 1.66054 × 10⁻²⁴ g = 1.66054 × 10⁻²⁷ kg. The pre-2019 SI treated this as a measured constant; the 2019 redefinition pinned Avogadro's number and made the equality exact.
When is this conversion used?
Any physics calculation that wants a per-atom mass in SI kilograms — de Broglie wavelengths, kinetic-theory speeds, single-molecule force-spectroscopy estimates. The conversion is the routine cast between atomic-scale data and SI-unit calculations.