Convert Foot to Light Year
Convert feet to light years instantly. 1 foot = 3.221739e-17 light year — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Light Year to Foot converter for the reverse conversion.
Units explained
Foot
A foot is an Imperial and US customary unit of length equal to 12 inches or exactly 0.3048 meters. It is the most commonly used unit of length in everyday measurement in the United States.
The foot's origin is literally the length of a human foot, used as a measurement standard since antiquity. The English foot was standardized at various points in history; the modern international foot (0.3048 m exactly) was fixed by the 1959 International Yard and Pound Agreement.
Feet are used in the US for body height, building dimensions, room sizes, road sign clearances, aviation altitude (feet above sea level), and most everyday distance estimation. The UK uses feet informally for height despite officially being metric.
Used since antiquity; standardized to 0.3048 m exactly by the International Yard and Pound Agreement of 1959. Aviation worldwide uses feet for altitude despite metric adoption elsewhere.
Light Year
A light year is the distance light travels in one Julian year in vacuum — exactly 9,460,730,472,580,800 meters (about 9.46×10¹⁵ m). It is the most common unit for expressing inter-stellar distances in non-technical astronomy.
Defined as the speed of light (299,792,458 m/s, exact) multiplied by one Julian year (365.25 days × 86400 seconds/day). Both factors are exact, making the light year exact by definition.
Light years are used in popular astronomy, science journalism, and stellar distance descriptions. The nearest star (Proxima Centauri) is 4.24 ly away; the Milky Way is about 100,000 ly across.
Concept of distance-as-time used since the 19th century; the modern exact definition follows from the 1983 SI definition of the meter via the speed of light.
Foot to Light Year conversion formula
The relationship between feet and light years:
To convert feet to light years, multiply the value in feet by 3.221739e-17. To reverse, multiply light years by 3.103914e+16.
How to use this converter
Type a value into the calculator. The result in light years updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Light Year to Foot converter for the reverse direction.
Step-by-step: convert feet to light years
- Write down the value in feet (ft).
- Multiply that value by the factor 3.221739e-17.
- The product is the equivalent value in light years (ly).
- To reverse, multiply the light year value by 3.103914e+16.
Worked examples
Example 1 — Convert 1 ft to ly:
1 × 3.221739e-17 = 3.221739e-17 ly
Example 2 — Convert 100 ft to ly:
100 × 3.221739e-17 = 3.221739e-15 ly
Real-world example — Reference scenario in case of fallback
Conversion between human-scale length units is the everyday workflow of architecture, athletics, and apparel design — three of the most common contexts that span metric and imperial systems.
1 ft × 3.221739e-17 = 3.221739e-17 ly
Real-world example — Adult height conversion
A 1.8-foot-tall person measures a value in light years that converts the height to the unit favoured by American forms, schools, or driver's licences. This is daily routine for anyone living between metric and imperial systems.
1.8 ft × 3.221739e-17 = 5.799129e-17 ly
Real-world example — Fabric purchase length
Two feet of fabric equals a value in light years essential for tailors and textile buyers sourcing material from international suppliers that quote in different units.
2 ft × 3.221739e-17 = 6.443477e-17 ly
Foot to Light Year conversion table
Standard reference values for converting feet to light years:
| Foot [ft] | Light Year [ly] |
|---|---|
| 0.01 | 3.221739e-19 |
| 0.1 | 3.221739e-18 |
| 1 | 3.221739e-17 |
| 2 | 6.443477e-17 |
| 3 | 9.665216e-17 |
| 4 | 1.288695e-16 |
| 5 | 1.610869e-16 |
| 10 | 3.221739e-16 |
| 20 | 6.443477e-16 |
| 30 | 9.665216e-16 |
| 40 | 1.288695e-15 |
| 50 | 1.610869e-15 |
| 100 | 3.221739e-15 |
| 500 | 1.610869e-14 |
| 1000 | 3.221739e-14 |
Frequently asked questions
How many light years is 1 foot?
How do I convert feet to light years?
How do I convert light years back to feet?
How many light years is 100 feet?
Popular length unit conversions
Convert Foot to other length units
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Metric / SI (18 units)
Imperial / US Customary (26 units)
Nautical (1 units)
Astronomical (9 units)
Atomic / Physics (6 units)
Typographic (3 units)
Sources & references
Conversion factor (1 ft = 3.221739e-17 ly) verified against the following authoritative sources:
- BIPM — The International System of Units (SI Brochure 9th ed.)
Official BIPM publication defining the seven SI base units (including the meter) and the rules for their use. The global authority on units of measurement.
- NIST — Guide to the SI
US National Institute of Standards and Technology reference covering the SI base and derived units with definitions and usage rules for US technical practice.
- NIST Special Publication 811 — Guide for the Use of the International System of Units
Detailed NIST guide covering exact conversion factors between SI and US customary units along with formatting and rounding conventions.
- NIST — Refinement of values for the yard and pound (Federal Register 1959)
The treaty (signed by US
- International Astronomical Union — System of Astronomical Constants
The IAU defines astronomical units including the AU (149597870700 m exactly) light-year and parsec used in astronomy and astrophysics.