How many atomic mass units are in 1 gram?

1 gram equals 6.022141e+23 atomic mass units, using the exact defined conversion factor rather than an estimate.

How do I convert gram to atomic mass unit?

Multiply the gram value by 6.022141e+23. The converter above does this instantly to whatever precision you set.

How do I convert atomic mass unit back to gram?

Use the reverse factor: 1 atomic mass unit equals 1.660539e-24 grams. You can also use the swap control in the converter above to flip the direction instantly.

Is the gram to atomic mass unit 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.

Grams to Atomic mass units Converter

Q: What is a gram?

Gram (g) measures mass. A gram is one-thousandth of a kilogram, the SI base unit of mass. It is classified as a SI derived (metric prefix) unit.

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).

About Converting Grams to Atomic mass units

Gram and Atomic mass unit 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. Gram is typically associated with standard small-mass unit worldwide, while Atomic mass unit is typically associated with used internationally in chemistry and physics, not a general-public unit.

Formula

atomic mass units = grams × 6.022141e+23

This factor comes from each unit's defined relationship to the category's base unit: 1 gram equals 0.001 base units, and 1 atomic mass unit equals 1.660539e-27 base units, so dividing one by the other gives the direct gram-to-atomic mass unit factor of 6.022141e+23.

Simple example

1 g × 6.022141e+23 = 6.022141e+23 u

1 gram = 6.022141e+23 atomic mass units.

Real-world example

10 g × 6.022141e+23 = 6.022141e+24 u

10 grams = 6.022141e+24 atomic mass units.

Conversion table

Gram (g)	Atomic mass unit (u)
0.001 g	6.022141e+20 u
0.01 g	6.022141e+21 u
1 g	6.022141e+23 u
10 g	6.022141e+24 u
100 g	6.022141e+25 u
1,000 g	6.022141e+26 u

Reverse conversion: Atomic mass unit to Gram

6.022141e+23 u × 1.660539e-24 = 1.00000004 g

6.022141e+23 atomic mass units = 1.00000004 grams.

grams = atomic mass units × 1.660539e-24

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

Gram vs. Atomic mass unit

Aspect	Gram	Atomic mass unit
Family	SI derived (metric prefix) unit	Non-SI unit accepted for use with SI (scientific)
Typical use	Cooking and nutrition labeling worldwide (including in the US, alongside ounces)	Expressing atomic and molecular masses in chemistry
Where it's used	Standard small-mass unit worldwide	Used internationally in chemistry and physics, not a general-public unit

Understanding the Gram

Gram (g) measures mass. A gram is one-thousandth of a kilogram, the SI base unit of mass. It is classified as a SI derived (metric prefix) unit.

Where it's used: Standard small-mass unit worldwide

Uses of the Gram today

Cooking and nutrition labeling worldwide (including in the US, alongside ounces)
Precious metal and small-item weighing
Scientific and laboratory measurement

History of the Gram

Originally defined in 1795 as the mass of one cubic centimeter of water, the gram follows directly from the kilogram (1/1000 of it) under the modern SI system, inheriting the kilogram's various historical and current definitions.

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

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.

Gram — sources

BIPM — The kilogram (SI base unit) — Basis for the gram as 1/1000 of the kilogram.

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.

Grams to Atomic mass units Converter — g to u

Scientific Units Converter