A gram is one thousandth of a kilogram.
Grams to Atomic mass units Converter — g to u
Convert Gram (g) to Atomic mass unit (u) using the exact conversion factor (1 gram = 6.022141e+23 atomic mass unit). See the formula, worked examples, conversion table, unit comparison, history, and common uses.
Grams to Atomic mass units converter
Converter
Mass/Weight Converter
Convert SI mass, imperial weight, jewelry, atomic, and astronomy mass units.
Context values
Some unit families need one extra value for a physically accurate result.
The unified atomic mass unit is used in atomic physics.
Result = input x 0.001 / 1.66053907e-27.
Mass uses the kilogram as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Grams to Atomic mass units
Weight conversions between Gram and Atomic mass unit come up constantly in everyday commerce, shipping, and cooking, since US packaging is usually labeled in pounds while most of the rest of the world uses kilograms. 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
50 g × 6.022141e+23 = 3.01107e+25 u
50 grams = 3.01107e+25 atomic mass units.
Conversion table
| Gram (g) | Atomic mass unit (u) |
|---|---|
| 1 g | 6.022141e+23 u |
| 5 g | 3.01107e+24 u |
| 10 g | 6.022141e+24 u |
| 25 g | 1.505535e+25 u |
| 50 g | 3.01107e+25 u |
| 100 g | 6.022141e+25 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.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
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.
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.
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).
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.
Where is the gram still used today?
Standard small-mass unit worldwide