How Speed Is Measured and Converted

Speed measures how fast something covers distance over time, and which unit you see depends heavily on context: road signs use km/h or mph, pilots and sailors use knots, and physics defaults to meters per second.

What Is Speed?

Speed is distance divided by time, expressed as a unit of length per unit of time. It answers “how fast,” as opposed to pace, which flips the question around to ask “how long per unit of distance” (covered in Understanding Pace).

Common Speed Units

• Kilometers per hour (km/h): road speeds in most of the world.
• Miles per hour (mph): road speeds in the US and UK.
• Meters per second (m/s): the standard unit in physics and science.
• Knots: nautical and aviation speed, based on the nautical mile.

Common Speed Conversions

Worked Example

Common Mistakes

• Confusing knots with mph. A knot (1.852 km/h) is close to but not the same as a mile per hour (1.60934 km/h); treating them as interchangeable introduces a real error over any meaningful distance.
• Mixing up speed and pace. Speed and pace measure the same underlying motion from opposite directions, and converting between them isn’t a simple unit swap, it requires inverting the ratio.
• Forgetting units when comparing figures. “60” means very different things as km/h, mph, and knots; always check the unit before comparing two speed figures.

Use the Speed Converter

The Speed Converter converts between km/h, mph, m/s, knots, and more instantly. If you’re working with running, cycling, or swimming pace specifically, see Understanding Pace.