How many kilograms are in 1 atomic mass unit?

1 atomic mass unit equals 1.660539e-27 kilograms, using the exact defined conversion factor rather than an estimate.

How do I convert atomic mass unit to kilogram?

Multiply the atomic mass unit value by 1.660539e-27. The converter above does this instantly to whatever precision you set.

How do I convert kilogram back to atomic mass unit?

Use the reverse factor: 1 kilogram equals 6.022141e+26 atomic mass units. You can also use the swap control in the converter above to flip the direction instantly.

Is the atomic mass unit to kilogram conversion exact?

Yes. The unified atomic mass unit is defined as exactly 1/12 the mass of a carbon-12 atom, approximately 1.6605390666 × 10⁻²⁷ kg. That fixed definition is what the converter above uses, so any rounding you see is a display choice, not a limitation of the math.

Why does this category span everything from atomic to astronomical scales?

Scientific work spans an enormous range of physical scales, from atomic distances (measured in angstroms or atomic mass units) to interstellar distances (measured in astronomical units or parsecs), so this category groups SI-derived and scale-specific units that researchers commonly need to convert between within their field.

Atomic mass units to Kilograms Converter

Q: What is a atomic mass unit?

Atomic mass unit (u) measures mass. The unified atomic mass unit is defined as exactly 1/12 the mass of a carbon-12 atom, approximately 1.6605390666 × 10⁻²⁷ kg. It is classified as a Non-SI unit accepted for use with SI (scientific).

Q: What is a kilogram?

Kilogram (kg) measures mass. The kilogram is the SI base unit of mass; every other SI mass unit is a decimal multiple or fraction of it. It is classified as a SI base unit.

About Converting Atomic mass units to Kilograms

Atomic mass unit and Kilogram are both scientific-measurement units, spanning everything from atomic and laboratory scales to astronomical distances — the kind of conversion that comes up constantly in physics, chemistry, and astronomy when a result needs to move between conventions used in different subfields. Atomic mass unit is typically associated with used internationally in chemistry and physics, not a general-public unit, while Kilogram is typically associated with used as the standard mass unit in nearly every country except the United States and a few others that primarily use the pound..

Formula

kilograms = atomic mass units × 1.660539e-27

This factor comes from each unit's defined relationship to the category's base unit: 1 atomic mass unit equals 1.660539e-27 base units, and 1 kilogram equals 1 base unit, so dividing one by the other gives the direct atomic mass unit-to-kilogram factor of 1.660539e-27.

Simple example

1 u × 1.660539e-27 = 1.660539e-27 kg

1 atomic mass unit = 1.660539e-27 kilograms.

Real-world example

10 u × 1.660539e-27 = 1.660539e-26 kg

10 atomic mass units = 1.660539e-26 kilograms.

Conversion table

Atomic mass unit (u)	Kilogram (kg)
0.001 u	1.660539e-30 kg
0.01 u	1.660539e-29 kg
1 u	1.660539e-27 kg
10 u	1.660539e-26 kg
100 u	1.660539e-25 kg
1,000 u	1.660539e-24 kg

Reverse conversion: Kilogram to Atomic mass unit

1.660539e-27 kg × 6.022141e+26 = 0.9999999599 u

1.660539e-27 kilograms = 0.9999999599 atomic mass units.

atomic mass units = kilograms × 6.022141e+26

For a page dedicated to this direction, see Kilogram to Atomic mass unit.

Atomic mass unit vs. Kilogram

Aspect	Atomic mass unit	Kilogram
Family	Non-SI unit accepted for use with SI (scientific)	SI base unit
Typical use	Expressing atomic and molecular masses in chemistry	Pricing and labeling goods sold by weight in retail and commodity trade
Where it's used	Used internationally in chemistry and physics, not a general-public unit	Used as the standard mass unit in nearly every country except the United States and a few others that primarily use the pound.

Understanding the Atomic mass unit

Atomic mass unit (u) measures mass. The unified atomic mass unit is defined as exactly 1/12 the mass of a carbon-12 atom, approximately 1.6605390666 × 10⁻²⁷ kg. It is classified as a Non-SI unit accepted for use with SI (scientific).

Where it's used: Used internationally in chemistry and physics, not a general-public unit

Uses of the Atomic mass unit today

Expressing atomic and molecular masses in chemistry
Nuclear and particle physics mass calculations
Molecular weight tables and mass spectrometry

History of the Atomic mass unit

Atomic mass scales existed before international standardization, using either oxygen-16 or natural oxygen as a reference. In 1961, the International Union of Pure and Applied Chemistry (IUPAC) and physicists agreed on a unified scale based on carbon-12, ending decades of divergent chemistry and physics mass scales.

The unified atomic mass unit (u), also called the dalton (Da) in SI-adjacent contexts, is now tied to the carbon-12 standard and remains the base unit for atomic and molecular mass tables used across chemistry and physics.

Historical origin. Atomic mass unit was not the invention of a single named person; it developed through the process described above.

Understanding the Kilogram

Kilogram (kg) measures mass. The kilogram is the SI base unit of mass; every other SI mass unit is a decimal multiple or fraction of it. It is classified as a SI base unit.

Where it's used: Used as the standard mass unit in nearly every country except the United States and a few others that primarily use the pound.

Uses of the Kilogram today

Pricing and labeling goods sold by weight in retail and commodity trade
Dosing calculations in medicine, especially for pediatric and weight-based prescriptions
Structural and material specification in metric-system engineering
Scientific measurement of mass across chemistry, physics, and materials research

History of the Kilogram

The kilogram's direct predecessor was the 'grave,' defined by the French Academy of Sciences in 1793 as the mass of one cubic decimeter of water at its temperature of maximum density. Because 'grave' echoed the aristocratic title 'graf,' revolutionary France's decree of 18 Germinal, Year III (7 April 1795) renamed the system: the gram became the reference unit, defined as the mass of one cubic centimeter of water at the melting point of ice, and the kilogram — one thousand grams — took over the grave's practical role.

Turning that water-based definition into a physical object required real experimental work: chemist Louis Lefèvre-Gineau was tasked in 1795 with measuring precisely how much a cubic decimeter of water weighed, and former royal jeweller Marc-Étienne Janety then fabricated a platinum cylinder to embody that measured mass. Deposited in the French National Archives in 1799, it became known as the Kilogramme des Archives.

The metric system spread unevenly — Napoleon briefly restricted its use — but France made it compulsory in 1840, and the 1875 Metre Convention (signed by seventeen nations including the US) established the BIPM and a shared international prototype. The platinum-iridium International Prototype of the Kilogram, adopted in 1889 and nicknamed 'Le Grand K,' served as the world's mass reference for over a century.

On 20 May 2019, the kilogram was redefined by fixing the Planck constant at exactly 6.62607015 × 10⁻³⁴ joule-seconds, so it can now be realized in a laboratory (via a Kibble balance) without reference to any physical object.

Historical origin. Kilogram was not the invention of a single named person; it developed through the process described above.

Atomic mass unit — sources

BIPM SI Brochure — Non-SI units accepted for use with SI — Lists the unified atomic mass unit and its carbon-12 definition.

Kilogram — sources

BIPM — The kilogram (SI base unit) — Official definition and history since the 2019 redefinition.
NIST — Kilogram: The Past — History of the kilogram standard from the grave to the International Prototype Kilogram.
SI Brochure, 9th edition (2019), Appendix 2 — BIPM — Official text of the Planck-constant-based definition of the kilogram.

Atomic mass units to Kilograms Converter — u to kg

Scientific Units Converter