Convert Meters to Astronomical Units - Length Converter
This tool converts a length given in metres to astronomical units (AU) using the authoritative IAU definition of the astronomical unit. The conversion uses fixed, exact values so the relationship between the two units is deterministic.
Use this converter for engineering, science, education, and documentation tasks. For measurements used in regulated or safety-critical contexts, follow applicable measurement and reporting standards and document uncertainty according to recognized guides.
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Methodology
The astronomical unit (AU) is defined by the International Astronomical Union (IAU) as exactly 149,597,870,700 metres. This exact definition is used as the conversion constant in the calculation.
Metre is the SI base unit of length. This converter applies the exact IAU constant and standard arithmetic division to produce the AU result from metres. Recommended best practice is to record the number of significant figures appropriate to the measurement and to state uncertainty when values originate from physical measurement.
Worked examples
Example 1: 1 metre = 1 / 149,597,870,700 AU ≈ 6.6845871226706e-12 AU.
Example 2: 149,597,870,700 metres = 1 AU exactly.
Example 3: 384,400,000 metres (approximate Earth–Moon distance) = 384400000 / 149597870700 ≈ 0.002571 AU.
Key takeaways
Conversion is direct and exact using the IAU definition: divide metres by 149,597,870,700 to get AU.
Report results with appropriate significant figures and document measurement uncertainty where relevant to your application.
Expert Q&A
What numeric constant is used for the conversion?
The converter uses the IAU definition: 1 AU = 149,597,870,700 metres (exact). This is the authoritative constant for converting metres to astronomical units.
Is the conversion exact or approximate?
The mathematical relationship is exact because the AU is defined as an exact integer number of metres by the IAU. Any approximation arises from rounding or from uncertainty in an input length measured in metres.
How should I report precision and uncertainty?
Follow measurement best practices such as documenting the number of significant figures and stating measurement uncertainty using guides from standards bodies. For traceable practice, see NIST and ISO guidance on units and uncertainty.
Are there limits to the values I can convert?
This converter will handle typical numeric inputs, but very large or very small values may be affected by floating-point limits of the environment in which it runs. For extremely large astronomical datasets, use arbitrary-precision tools or software designed for high dynamic range and document numeric precision.
Where can I find authoritative references for these units and practices?
See the citation list included below for links to the IAU definition and standards organizations that publish guidance on units, measurement uncertainty, and reporting practices.
Sources & citations
- IAU Resolutions (IAU 2012) - definition of the astronomical unit — https://www.iau.org/static/resolutions/IAU2012_English.pdf
- NIST: Metric System and SI units guidance — https://www.nist.gov/pml/weights-and-measures/metric-si
- ISO: International Organization for Standardization — https://www.iso.org
- IEEE: Institute of Electrical and Electronics Engineers — https://www.ieee.org
- OSHA: Occupational Safety and Health Administration — https://www.osha.gov