The speed of light in vacuum, commonly denoted c, is a universal physical constant important in many areas of physics. Its exact value is 299,792,458 metres per second (approximately 3.00×108 m/s, or 186,282 mi/s); it is exact because the unit of length, the metre, is defined from this constant and the international standard for time.
| Definition | Relation to SI units |
|---|---|
≡ 299792458 m/s |
| yard per hour | inch per minute | yard per minute | foot per minute | inch per hour | inch per second | mile per minute | foot per hour |
|---|---|---|---|---|---|---|---|
| 1 | 0.6 | 0.0166667 | 0.05 | 36 | 0.01 | 9.469696969697 × 10-6 | 3 |
| 1.6666667 | 1 | 0.0277778 | 0.0833333 | 60 | 0.0166667 | 1.5782828282828 × 10-5 | 5 |
| 60 | 36 | 1 | 3 | 2 160 | 0.6 | 0.0005682 | 180 |
| 20 | 12 | 0.3333333 | 1 | 720 | 0.2 | 0.0001894 | 60 |
| 0.0277778 | 0.0166667 | 0.0004630 | 0.0013889 | 1 | 0.0002778 | 2.6304713804714 × 10-7 | 0.0833333 |
| 100 | 60 | 1.6666667 | 5 | 3 600 | 1 | 0.0009470 | 300 |
| 105 600 | 63 360 | 1 760 | 5 280 | 3 801 600 | 1 056 | 1 | 316 800 |
| 0.3333333 | 0.2 | 0.0055556 | 0.0166667 | 12 | 0.0033333 | 3.1565656565657 × 10-6 | 1 |
| Symbol | Definition |
|---|---|
| ≡ | exactly equal |
| ≈ | approximately equal to |
| = | equal to |
| digits | indicates that digits repeat infinitely (e.g. 8.294 369 corresponds to 8.294 369 369 369 369 …) |
| 1 speed of lights | = 299792458 meters per second |
| 2 speed of lights | = 599584916 meters per second |
| 3 speed of lights | = 899377374 meters per second |
| 4 speed of lights | = 1199169832 meters per second |
| 5 speed of lights | = 1498962290 meters per second |