Convert kilometers per second to kilometers per hour easily.

Speed conversions don’t have to feel like rocket science, even when dealing with units as different as kilometers per second (km/s) and kilometers per hour (km/h). Whether you’re calculating spacecraft velocities or just curious about how fast your favorite sci-fi ship would go in more familiar terms, this guide breaks down the math, history, and quirks of these two units. Let’s get started.

Unit definitions

What is a kilometer per second (km/s)?

A kilometer per second measures speed as the number of kilometers traveled in one second. It’s part of the metric system and is used primarily in scientific contexts where extreme speeds are involved. For example, the Earth orbits the Sun at about 29.78 km/s.

• Symbol: km/s
• Common uses: Astronomy, physics, ballistics
• Definition: 1 km/s = 1000 meters per second

What is a kilometer per hour (km/h)?

Kilometers per hour measures how many kilometers are covered in one hour. It’s the standard speed unit for road traffic in most countries outside the US. Your car’s speedometer likely shows km/h.

• Symbol: km/h
• Common uses: Automotive speeds, weather reports, sports
• Definition: 1 km/h = 0.27778 meters per second

Conversion formula

To convert km/s to km/h:
km/h = km/s × 3600

Since there are 3600 seconds in an hour (60 seconds × 60 minutes), multiplying km/s by 3600 scales the speed to an hourly rate.

Example calculations

1. Converting 1 km/s to km/h:
   1 km/s × 3600 = 3600 km/h
   (That’s faster than a commercial jet’s cruising speed!)
2. Converting 0.025 km/s to km/h:
   0.025 km/s × 3600 = 90 km/h
   (A brisk highway speed in many countries.)

Conversion tables

Kilometers per second to kilometers per hour

Kilometers per hour to kilometers per second

Historical background

The kilometer became a standard unit during the French Revolution, part of the metric system’s push for decimal based measurements. While km/h gained traction with the rise of automobiles in the 20th century, km/s remained confined to scientific circles. Early 19th-century astronomers first used km/s to describe celestial motions, like the speed of comets. Meanwhile, km/h became a practical choice for trains and cars, balancing precision with everyday usability. Interestingly, some early speedometers displayed both mph and km/h before standardization took hold.

Interesting facts

1. Earth’s orbital speed: Our planet zips around the Sun at 29.78 km/s, or about 107,200 km/h.
2. Speed of sound: In dry air at 20°C, sound travels at roughly 0.343 km/s (1234.8 km/h).
3. Spacecraft re-entry: The Apollo capsules re-entered Earth’s atmosphere at nearly 11 km/s (39,600 km/h).
4. Bullet speeds: A typical rifle bullet moves at about 0.9 km/s (3240 km/h).
5. Light speed: While light travels at 299,792 km/s , converting that to km/h would give a staggering 1,079,252,848.8 km/h.

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