Speed Converter

Speed shapes nearly every aspect of our world — from a cheetah’s sprint to a spacecraft soaring through space. Speed conversion helps us make sense of how fast things move by translating between units like miles per hour, kilometers per hour, knots, and meters per second. Whether you’re a student studying physics, a traveler switching between metric and imperial systems, or a scientist measuring velocities beyond Earth, understanding speed gives you a new lens through which to view the world. This guide goes beyond simple math to explore the science, real-life stories, and fascinating facts behind speed — and how it influences everything from technology travel.

Want to go deeper? Try the Force Converter to see how speed connects with mass and acceleration. Or explore the Pressure Converter,

 especially if you're interested in weather systems or fluid dynamics, where pressure and velocity go hand in hand.

What Is Speed?

Think back to the last time you rushed to catch a bus or watched an airplane slicing through the sky. Whether you noticed or not, you were witnessing speed in motion. At its core, speed is a way to describe how quickly something moves from one point to another. Scientists define it as the distance traveled divided by the time it takes¹, but you don’t need to be a physicist to recognize its impact.

One key distinction that often causes confusion: speed and velocity aren't identical. Speed tells you how fast something is going, but velocity includes the direction of movement as well. For instance, if you’re driving at 60 kilometers per hour, that’s your speed. But if you’re moving at 60 kilometers per hour heading north, now you’re talking about velocity.

The formula to calculate speed is straightforward:

Speed = Distance : Time

Naturally, not everything moves at the same pace. Humans can run around 10–12 meters per second, but satellites orbit Earth at astonishing speeds — often thousands of meters per second². Once you leave the surface, speed ramps up quickly.

But speed isn’t just about numbers. It plays a critical role in real-world applications: from building safer roads and engineering high-speed trains to launching spacecraft into orbit. Understanding how speed works — and how to convert it across different units — is essential for innovation, safety, and progress in both science and daily life.

Common Speed Units 

When it comes to speed, no single unit fits every situation. A race car, a ship, a spacecraft — each world measures motion a little differently. That’s why speed conversion is so important: it helps scientists, engineers, travelers, and even athletes make sense of motion, no matter which units they're using.

Here’s a closer look at the many ways we measure speed around the world — from everyday travel to cosmic adventures.

Need to convert across systems? Try the all-in-one Unit Converter to handle dozens of measurement categories — instantly and accurately.

Everyday Speed Units

• Meter per second (m/s) – Standard unit in science and engineering

• Kilometers per hour (km/h) – Common in most countries for road speed limits

• Miles per hour (mi/h) – Used mainly in the United States and the UK

• Foot per second (ft/s) – Used occasionally in technical fields

• Foot per minute (ft/min) – Used for slower mechanical processes

• Yard per hour (yd/h), Yard per minute (yd/min), Yard per second (yd/s) – Less common, but seen in traditional measurements

Maritime and Aviation Units

• Knot (kt, kn) – Nautical speed, equal to one nautical mile per hour

• Knot (UK) [kt (UK)] – Slight regional variation

Scientific and Extreme Speed Units

• Velocity of light in vacuum – Roughly 299,792,458 meters per second³

• Cosmic velocity – first, second, third – Speeds needed to orbit or escape Earth's gravity

• Earth’s velocity – Earth's movement around the sun: about 30 km/s

Other Specialized Units

• Meter/hour (m/h)

• Meter/minute (m/min)

• Kilometer/minute (km/min)

• Kilometer/second (km/s)

• Centimeter/hour (cm/h)

• Centimeter/minute (cm/min)

• Centimeter/second (cm/s)

• Millimeter/hour (mm/h)

• Millimeter/minute (mm/min)

• Millimeter/second (mm/s)

• Foot/hour (ft/h)

Speeds Related to Sound

• Velocity of sound in pure water – About 1,480 m/s⁴

• Velocity of sound in sea water (20°C, 1 atm) – About 1,500 m/s

• Mach (SI standard) – Speed relative to the speed of sound at a given condition (typically about 343 m/s at sea level)

The Race Against the Speed of Sound

In the late 1940s, there was a moment when going faster than the speed of sound felt almost... impossible. Planes would shake violently as they approached what pilots called "the sound barrier," and many believed it was a limit humans were simply not meant to cross.

But Chuck Yeager, a young U.S. Air Force pilot with a fearless spirit, thought differently. On October 14, 1947, flying an orange, rocket-powered aircraft called the Bell X-1, Yeager did what no one else had done before: he broke the sound barrier, reaching a speed of about 1.06 Mach — faster than the speed of sound at sea level.

It wasn't just a technical achievement. It was a human one. Yeager had broken not just a physical limit, but a mental one — the belief that some speeds were "too dangerous" to pursue. His success electrified the world and opened the door to the era of supersonic flight, space exploration, and a whole new understanding of what speed could mean.

After Yeager’s flight, Mach numbers — named after physicist Ernst Mach, who studied shock waves — became a common way to express speeds beyond the speed of sound. Saying "Mach 1" meant moving at the speed of sound; "Mach 2" meant twice that speed, and so on. Today, we hear "Mach" not only in aviation and space contexts but even in popular culture, a reminder of how deeply that 1947 moment shaped the way we think about speed.

In many ways, Chuck Yeager’s flight wasn’t just about a plane flying fast. It symbolized the timeless human desire to push past limits — to take something everyone believed was impossible and prove it could be done.

Cosmic Speeds

When we talk about speed, we usually think about cars, planes, or maybe a sprint at the Olympics. But once you leave Earth, speed means survival — and exploration.

Scientists have special names for the speeds you need to reach if you want to stay in orbit, escape Earth, or even leave the Solar System completely. They call them the first, second, and third cosmic velocities.

• The first cosmic velocity is about 7.9 kilometers per second (km/s).
  That’s the speed a spacecraft needs just to stay circling Earth without falling back. It's the speed satellites and the International Space Station are hitting every single second as they orbit above us.

• The second cosmic velocity clocks in at 11.2 km/s.
  If you want to leave Earth entirely — like the missions heading to Mars — you need this much speed to break free from our planet’s gravitational grip.

• The third cosmic velocity is a whopping 16.7 km/s.
  This is the speed you’d need to escape the Sun’s pull from Earth’s orbit and travel into the vast openness of the galaxy — exactly what Voyager 1 and Voyager 2 have done.

How Fast Is Sound in Sea Water?

When we think of sound, most of us picture voices traveling through the air — maybe across a room, or down a hallway.

But underwater, sound behaves like a superhero. In sea water, sound moves at about 1,500 meters per second (m/s)”. That’s over four times faster than it travels through air!

The reason? Water is much denser than air, and its particles are packed closer together, making it easier for vibrations to pass along quickly.
This is why:

• Submarines can detect other objects from kilometers away.

• Dolphins and whales can “talk” to each other across incredible distances.

• Scientists use sonar to map the ocean floor with incredible detail.

Next time you imagine the deep sea, think of it not as a silent world — but one full of messages traveling faster than anything you’ve ever heard above the waves.