The unified atomic mass unit is used in atomic physics.
Atomic mass units to Grams Converter — u to g
Convert Atomic mass unit (u) to Gram (g) using the exact conversion factor (1 atomic mass unit = 1.660539e-24 gram). See the formula, worked examples, conversion table, unit comparison, history, and common uses.
Atomic mass units to Grams 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.
A gram is one thousandth of a kilogram.
Result = input x 1.66053907e-27 / 0.001.
Mass uses the kilogram as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Atomic mass units to Grams
Weight conversions between Atomic mass unit and Gram 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. Atomic mass unit is typically associated with used internationally in chemistry and physics, not a general-public unit, while Gram is typically associated with standard small-mass unit worldwide.
Formula
grams = atomic mass units × 1.660539e-24
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 gram equals 0.001 base units, so dividing one by the other gives the direct atomic mass unit-to-gram factor of 1.660539e-24.
Simple example
1 u × 1.660539e-24 = 1.660539e-24 g
1 atomic mass unit = 1.660539e-24 grams.
Real-world example
50 u × 1.660539e-24 = 8.302695e-23 g
50 atomic mass units = 8.302695e-23 grams.
Conversion table
| Atomic mass unit (u) | Gram (g) |
|---|---|
| 1 u | 1.660539e-24 g |
| 5 u | 8.302695e-24 g |
| 10 u | 1.660539e-23 g |
| 25 u | 4.151348e-23 g |
| 50 u | 8.302695e-23 g |
| 100 u | 1.660539e-22 g |
Reverse conversion: Gram to Atomic mass unit
1.660539e-24 g × 6.022141e+23 = 0.9999999599 u
1.660539e-24 grams = 0.9999999599 atomic mass units.
atomic mass units = grams × 6.022141e+23
For a page dedicated to this direction, see Gram to Atomic mass unit.
Atomic mass unit vs. Gram
| Aspect | Atomic mass unit | Gram |
|---|---|---|
| Family | Non-SI unit accepted for use with SI (scientific) | SI derived (metric prefix) unit |
| Typical use | Expressing atomic and molecular masses in chemistry | Cooking and nutrition labeling worldwide (including in the US, alongside ounces) |
| Where it's used | Used internationally in chemistry and physics, not a general-public unit | Standard small-mass unit worldwide |
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 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.
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.
Gram — sources
- BIPM — The kilogram (SI base unit) — Basis for the gram as 1/1000 of the kilogram.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many grams are in 1 atomic mass unit?
1 atomic mass unit equals 1.660539e-24 grams, using the exact defined conversion factor rather than an estimate.
How do I convert atomic mass unit to gram?
Multiply the atomic mass unit value by 1.660539e-24. The converter above does this instantly to whatever precision you set.
How do I convert gram back to atomic mass unit?
Use the reverse factor: 1 gram equals 6.022141e+23 atomic mass units. You can also use the swap control in the converter above to flip the direction instantly.
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).
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.
Is the atomic mass unit to gram 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 atomic mass unit still used today?
Used internationally in chemistry and physics, not a general-public unit