# How do I convert amu to kg?

Converts atomic mass units (u) to kilograms (kg) and back, with the CODATA 2022 atomic mass unit.

- Page: https://www.acalculator.org/convert/amu-to-kg
- JSON spec: https://www.acalculator.org/convert/amu-to-kg.json
- Version: fc3abbeea28e

## Default answer

Example with the default inputs (Atomic mass units (u) 1): 1 u = 1.66054 × 10⁻²⁷ kg.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| value | Atomic mass units (u) | The amount in atomic mass units to convert. |
| result | Kilograms (kg) | The same amount in kilograms. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| value | Atomic mass units (u) | The amount in atomic mass units to convert. |
| result | Kilograms (kg) | The amount in kilograms. |

## Method

kg = u × 1.66053906892 × 10⁻²⁷

## Assumptions

- 1 u (unified atomic mass unit, or dalton) = 1.66053906892 × 10⁻²⁷ kg, the CODATA 2022 recommended value (NIST); it is measured, with a standard uncertainty of 0.00000000052 × 10⁻²⁷ kg (3.1 parts in 10¹⁰). The page converts with this value as if exact.
- Exact on the typed decimals: the answer shows 6 significant digits as d.ddddd × 10ⁿ (trailing zeros dropped), rounded half up; 0 shows as 0. A value above 0 whose answer is below 10⁻³⁰⁰ gives no answer.

## Worked examples

1. value = 1 gives result = 1.66054 × 10⁻²⁷. Source: NIST CODATA 2022 value of the atomic mass unit (https://physics.nist.gov/cgi-bin/cuu/Value?ukg).
2. value = 12 gives result = 1.99265 × 10⁻²⁶. Source: NIST CODATA 2022 value of the atomic mass unit (https://physics.nist.gov/cgi-bin/cuu/Value?ukg).

## FAQ

### How many kg is 1 amu?

1.66053906892 × 10⁻²⁷ kg, the CODATA 2022 value of the unified atomic mass unit (u), also called the dalton (Da). The page shows it to 6 significant digits: 1.66054 × 10⁻²⁷ kg.

### How do I convert amu to kg?

Multiply by 1.66053906892 × 10⁻²⁷: kg = u × 1.66053906892 × 10⁻²⁷. So 12 u, the mass of one carbon-12 atom, is 1.99265 × 10⁻²⁶ kg, and 1,000 u is 1.66054 × 10⁻²⁴ kg.

### Is the conversion exact?

No. The atomic mass unit is measured: CODATA 2022 gives a standard uncertainty of 0.00000000052 × 10⁻²⁷ kg, 3.1 parts in 10¹⁰. That is far below the 6 significant digits the page shows. The page converts with the recommended value as if it were exact.

### How do I convert kg back to amu?

Divide by 1.66053906892 × 10⁻²⁷, or type the kilograms into the second box. 1 kg is about 6.022141 × 10²⁶ u.

### What values can I convert?

From 0 to 1,000,000,000,000 u (10¹²), which is 1.66054 × 10⁻¹⁵ kg; a larger value gives no answer. A value above 0 whose answer is below 10⁻³⁰⁰ kg (below about 6.022 × 10⁻²⁷⁴ u) gives no answer either: "The answer is below 10⁻³⁰⁰, too small to show. Enter a larger value."

## Sources

- NIST SP 811 (2008), Guide for the Use of the International System of Units, Appendix B.8: Factors for Units Listed Alphabetically (bold factors are exact), retrieved 2026-10-18. https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8
- NIST, CODATA Internationally Recommended 2022 Values of the Fundamental Physical Constants: unified atomic mass unit, 1.660 539 068 92(52) × 10⁻²⁷ kg, relative standard uncertainty 3.1 × 10⁻¹⁰, retrieved 2026-10-19. https://physics.nist.gov/cgi-bin/cuu/Value?ukg