Speed of light in a vacuum is 1,079,252,848.8 kilometres per hour.

The speed of light is a fundamental constant denoted by c, and in a vacuum, it travels at approximately 1.08×10⁹ km/h or 299,792,458 meters per second. To express this in kilometers per hour, you can use the following conversion factors: 1 kilometer is equal to 1, 000 meters, and 1 hour is equal to 3, 600 seconds.

c ≈ 1,079,252,848.8 km/h

c ≈ (299,792,458 m/s) × 1 km/1000 m × 3600 s/1 h

After performing the calculation, the speed of light in kilometres per hour is approximately 1.08 × 10⁹  km/h. This speed is an absolute constant in a vacuum and represents the maximum speed at which information or energy can be transmitted in the universe.