Convert Light Year to Foot
Convert light years to feet instantly. 1 light year = 3.103914e+16 foot — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Foot to Light Year converter for the reverse conversion.
Units explained
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
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 to Foot conversion formula
The relationship between light years and feet:
To convert light years to feet, multiply the value in light years by 3.103914e+16. To reverse, multiply feet by 3.221739e-17.
How to use this converter
Type a value into the calculator. The result in feet updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Foot to Light Year converter for the reverse direction.
Step-by-step: convert light years to feet
- Write down the value in light years (ly).
- Multiply that value by the factor 3.103914e+16.
- The product is the equivalent value in feet (ft).
- To reverse, multiply the foot value by 3.221739e-17.
Worked examples
Example 1 — Convert 1 ly to ft:
1 × 3.103914e+16 = 3.103914e+16 ft
Example 2 — Convert 100 ly to ft:
100 × 3.103914e+16 = 3.103914e+18 ft
Light Year to Foot conversion table
Standard reference values for converting light years to feet:
| Light Year [ly] | Foot [ft] |
|---|---|
| 0.01 | 3.103914e+14 |
| 0.1 | 3.103914e+15 |
| 1 | 3.103914e+16 |
| 2 | 6.207828e+16 |
| 3 | 9.311743e+16 |
| 4 | 1.241566e+17 |
| 5 | 1.551957e+17 |
| 10 | 3.103914e+17 |
| 20 | 6.207828e+17 |
| 30 | 9.311743e+17 |
| 40 | 1.241566e+18 |
| 50 | 1.551957e+18 |
| 100 | 3.103914e+18 |
| 500 | 1.551957e+19 |
| 1000 | 3.103914e+19 |
Frequently asked questions
How many feet is 1 light year?
How do I convert light years to feet?
How do I convert feet back to light years?
How many feet is 100 light years?
Popular length unit conversions
Convert Light Year to other length units
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Metric / SI (4 units)
Imperial / US Customary (4 units)
Astronomical (8 units)
Sources & references
Conversion factor (1 ly = 3.103914e+16 ft) 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.