Speed of light in vacuum (c)
Exactly 299 792 458 meters per second.
What is the speed of light?
- Symbol
- c
- Quantity
- Speed
- Unit system
- SI
- Definition
- Exactly 299 792 458 meters per second.
- Exact
- Yes, the value is exact by definition
- Source
- SI Brochure, 9th edition (BIPM, 2019)
Common applications
A fixed physical constant (exactly 299,792,458 m/s), used in physics and astronomy as a reference speed.
Speed of light in vacuum in other speed units
- 1 c = 29979245800 cm/sCentimeter per second
- 1 c = 299792458 m/sMeter per second
- 1 c = 1079252848.8 km/hKilometer per hour
- 1 c = 299792.458 km/sKilometer per second
- 1 c ≈ 670616629.4 mphMile per hour
- 1 c ≈ 983571056.4 ft/sFoot per second
- 1 c ≈ 582749918.4 knKnot
Speed of light in vacuum quick reference
| Speed of light in vacuum | Kilometer per hour | Mile per hour | Centimeter per second |
|---|---|---|---|
| 1 c | = 1079252848.8 km/h | ≈ 670616629.4 mph | = 29979245800 cm/s |
| 10 c | = 10792528488 km/h | ≈ 6706166294 mph | = 299792458000 cm/s |
| 100 c | = 107925284880 km/h | ≈ 67061662940 mph | = 2997924580000 cm/s |
| 1000 c | = 1079252848800 km/h | ≈ 670616629400 mph | = 29979245800000 cm/s |
Where the speed of light fits
The next smaller speed unit is the kilometer per second (km/s). 1 c = 299792.458 km/s, and 1 km/s ≈ 0.000003335640952 c.
Frequently asked questions
- How many kilometers per hour are in one speed of light?
- One speed of light = 1079252848.8 km/h (kilometers per hour).
- How many miles per hour are in one speed of light?
- One speed of light ≈ 670616629.4 mph (miles per hour).
- How many centimeters per second are in one speed of light?
- One speed of light = 29979245800 cm/s (centimeters per second).