A foot is exactly 0.3048 meters.
Feet to Light-years Converter — ft to ly
Convert Foot (ft) to Light-year (ly) using the exact conversion factor (1 foot = 3.221739e-17 light-year). See the formula, worked examples, conversion table, unit comparison, history, and common uses.
Feet to Light-years converter
Converter
Length Converter
Convert SI, imperial, US customary, astronomical, scientific, and historical length units.
Context values
Some unit families need one extra value for a physically accurate result.
A light-year is the distance light travels in a Julian year.
Result = input x 0.3048 / 9.46073047e+15.
Length uses the meter as the base unit.
Reserved above the conversion cards and below the converter.
About Converting Feet to Light-years
Foot and Light-year both measure length. Foot is typically associated with united States (height, construction, aviation altitude), while Light-year is typically associated with used internationally in astronomy and popular science for interstellar distances..
Formula
light-years = feet × 3.221739e-17
This factor comes from each unit's defined relationship to the category's base unit: 1 foot equals 0.3048 base units, and 1 light-year equals 9.46073e+15 base units, so dividing one by the other gives the direct foot-to-light-year factor of 3.221739e-17.
Simple example
1 ft × 3.221739e-17 = 3.221739e-17 ly
1 foot = 3.221739e-17 light-years.
Real-world example
10 ft × 3.221739e-17 = 3.221739e-16 ly
10 feet = 3.221739e-16 light-years.
Conversion table
| Foot (ft) | Light-year (ly) |
|---|---|
| 1 ft | 3.221739e-17 ly |
| 5 ft | 1.610869e-16 ly |
| 10 ft | 3.221739e-16 ly |
| 21.0975 ft | 6.797063e-16 ly |
| 42.195 ft | 1.359413e-15 ly |
| 100 ft | 3.221739e-15 ly |
Reverse conversion: Light-year to Foot
3.221739e-17 ly × 3.103914e+16 = 1.000000142 ft
3.221739e-17 light-years = 1.000000142 feet.
feet = light-years × 3.103914e+16
For a page dedicated to this direction, see Light-year to Foot.
Foot vs. Light-year
| Aspect | Foot | Light-year |
|---|---|---|
| Family | US/imperial customary unit | Non-SI unit (astronomical) |
| Typical use | Height measurement in the US and UK | Measuring distances to stars and galaxies |
| Where it's used | United States (height, construction, aviation altitude) | Used internationally in astronomy and popular science for interstellar distances. |
Understanding the Foot
Foot (ft) measures distance. The international foot is defined as exactly 0.3048 meters. It is classified as a US/imperial customary unit.
Where it's used: United States (height, construction, aviation altitude) United Kingdom (height, some construction contexts)
Uses of the Foot today
- Height measurement in the US and UK
- US construction and real estate (square footage)
- Aviation altitude worldwide (feet remain standard even in metric countries)
History of the Foot
The foot has ancient roots (Roman 'pes', various regional English feet), standardized into the modern English foot over centuries. The international foot (exactly 0.3048 m) was fixed by the 1959 International Yard and Pound Agreement, resolving small historical differences between US and UK measurements.
Historical origin. Foot was not the invention of a single named person; it developed through the process described above.
Understanding the Light-year
Light-year (ly) measures distance. A light-year is the distance light travels in one Julian year (365.25 days) in vacuum: exactly 9,460,730,472,580,800 meters. It is classified as a Non-SI unit (astronomical).
Where it's used: Used internationally in astronomy and popular science for interstellar distances.
Uses of the Light-year today
- Measuring distances to stars and galaxies
- Popular science communication about the scale of the universe
- Astrophysics research
History of the Light-year
The light-year emerged in 19th-century astronomy as scientists began measuring stellar distances via parallax (Friedrich Bessel's 1838 measurement of 61 Cygni is often cited as the first reliable stellar distance). Expressing these vast distances in light-travel-time became a practical convention, and the unit's value follows directly from the defined speed of light and the length of a Julian year.
Historical origin. Light-year was not the invention of a single named person; it developed through the process described above.
Foot — sources
- NIST — International yard and pound (1959) — Fixes the modern foot at exactly 0.3048 meters.
Light-year — sources
- IAU — Light year definition — Defines the light-year via the Julian year and the speed of light.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many light-years are in 1 foot?
1 foot equals 3.221739e-17 light-years, using the exact defined conversion factor rather than an estimate.
How do I convert foot to light-year?
Multiply the foot value by 3.221739e-17. The converter above does this instantly to whatever precision you set.
How do I convert light-year back to foot?
Use the reverse factor: 1 light-year equals 3.103914e+16 feet. You can also use the swap control in the converter above to flip the direction instantly.
What is a foot?
Foot (ft) measures distance. The international foot is defined as exactly 0.3048 meters. It is classified as a US/imperial customary unit.
What is a light-year?
Light-year (ly) measures distance. A light-year is the distance light travels in one Julian year (365.25 days) in vacuum: exactly 9,460,730,472,580,800 meters. It is classified as a Non-SI unit (astronomical).
Is the foot to light-year conversion exact?
Yes. A light-year is the distance light travels in one Julian year (365.25 days) in vacuum: exactly 9,460,730,472,580,800 meters. That fixed definition is what the converter above uses, so any rounding you see is a display choice, not a limitation of the math.
Where is the foot still used today?
United States (height, construction, aviation altitude) United Kingdom (height, some construction contexts)