Type one distance, read it as light-years, parsecs, AU, light-seconds, km and miles at once, all in your browser
- Runs locally
- Category Format Converter
- Best for Turning pasted content or local files into a handoff-friendly format.
- Light-year (ly)1
- Parsec (pc)0.306597988717
- Astronomical unit (AU)63239.973262
- Light-hour8766
- Light-minute525960
- Light-second31557600
- Kilometre (km)9.4607e+12
- Mile (mi)5.878606e+12
What this tool does
A free light year converter that turns any astronomical distance into every other common unit at the same time. Enter a value in light-years, parsecs, astronomical units, light-hours, light-minutes, light-seconds, kilometres or miles, and the tool fills in all the rest instantly. It uses the standard constants: one light-year is 9.4607 trillion kilometres (the distance light travels in one Julian year), one parsec is 3.2616 light-years, and one astronomical unit is 149.6 million kilometres. The light-second, light-minute and light-hour are derived from the same light-year figure, so every ratio stays self-consistent. Preset reference distances let you jump straight to Proxima Centauri at 4.2465 light-years, Sirius, the galactic centre or the Andromeda Galaxy. Copy any single row or the whole set with one click, and share the URL to reopen the exact same value and unit. Everything runs client-side, nothing is uploaded.
Tool details
- Input
- Numbers
- The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
- Output
- Live result + Copy
- The result area focuses on usable output, with copy, download, or preview actions when supported.
- Privacy
- Browser-side processing
- The main tool logic does not call an external API, so inputs normally stay in the current tab.
- Save / share
- Shareable URL state
- Key settings are encoded in the URL so another person can reopen the same setup.
- Performance budget
- Initial JS <= 9 KB
- No WASM budget is declared, keeping the tool quick to open on mobile.
- Best fit
- Format Converter · Student
- Category and role tags drive related tools, internal links, and quick fit checks.
How to use
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1. Input
Paste or drop your content into the tool panel.
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2. Process
Click the button. All processing is local in your browser.
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3. Copy / Download
Copy the result or download to disk in one click.
How Light Year Converter fits into your work
Use it when the main problem is getting content from one practical format into another.
Conversion jobs
- Turning pasted content or local files into a handoff-friendly format.
- Previewing a conversion before you use it in a larger workflow.
- Cleaning small format mismatches without opening a full editor.
Conversion checks
- Try a small sample first when the source format is messy.
- Check character encoding, separators, and line endings after conversion.
- Keep the source until the converted output has been reviewed.
Good next steps
These links move the current task into a more complete workflow.
- 1 Unit Converter Convert between length, weight, temperature, area, volume, speed, time — instant, browser-only Open
- 2 Scientific Calculator Scientific calculator — sin / cos / log / sqrt / power, with full keyboard input + history, deg/rad mode. Open
- 3 Scientific Notation Converter Plain ⇄ scientific (a×10ⁿ) ⇄ engineering ⇄ E-notation — with significant figures, exact big/small numbers — browser-only Open
Real-world use cases
Make sense of star distances in the news
A headline says a newly found exoplanet is 40 light-years away and you want that in something tangible. Type 40 in light-years and read it instantly as about 3.78e14 km, 12.3 parsecs, or 2.5 million AU. Now the number means something: it is far past every probe humanity has launched, yet close enough that the host star is naked-eye faint on a dark night.
Check homework and exam answers in astronomy class
A physics problem asks how many kilometres are in 3.5 light-years. Enter 3.5 ly and the kilometre row shows the answer, while the parsec and AU rows let you verify the other parts of a multi-step question. Students see every conversion side by side instead of chaining error prone multiplications by hand, and teachers can build worked examples in seconds.
Size up a solar system orbit in AU
You are sketching the outer planets and need their distances in a single unit. Switch the selector to astronomical units and type the orbit radius; the tool shows it in light-minutes too, so you can label your diagram with both the AU figure astronomers use and the travel time that makes the scale intuitive to a general audience.
Sanity-check a science fiction travel time
Writing a story where a ship crosses to Proxima Centauri, you want the distance to stay plausible. Load the Proxima preset at 4.2465 light-years, read it as light-seconds and kilometres, then divide by your fictional ship speed. The light-second view makes it obvious how slow even fast spacecraft are compared with light itself.
Common pitfalls
Treating a light-year as a length of time. It measures distance, so a phrase like it happened many light-years ago is wrong. If you mean duration, you want years, not light-years, and this tool will not help with that.
Confusing parsecs and light-years, or assuming they are equal. One parsec is 3.2616 light-years, not one, so a 10 parsec object is about 32.6 light-years away. Always check which unit a source quotes before plugging the number in.
Forgetting that AU and light-years differ by tens of thousands. One light-year is about 63241 AU, so mixing them up by even one unit slot turns a planetary distance into an interstellar one. Pick the unit in the selector deliberately, do not assume.
Privacy
Every conversion runs as plain JavaScript inside your browser tab. The value you type and the unit you pick never leave the page, and nothing is logged or uploaded. The one caveat: the value and unit are stored in the shareable URL query string, so a link you paste into chat will record those two numbers in the recipient server access log. Since this tool only handles public astronomical distances, that is rarely a concern, but it is worth knowing how the share link works.
FAQ
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