Home›Glossary›Speed

Speed

General

Speed (Physics)

How fast an object is moving, measured as total distance traveled divided by time elapsed — a scalar quantity with magnitude only, unlike velocity which also has direction.

Written by · Reviewed by the thecalcu.com team · Last updated July 6, 2026

What is Speed?

Speed measures how fast an object is moving, calculated simply as the total distance traveled divided by the time elapsed. It's a scalar quantity, it has magnitude (a number) but no direction, which distinguishes it from velocity, a vector quantity that also accounts for direction via displacement.

The Speed Calculator computes speed directly from a distance and time input, with unit conversion support for km/h, mph, and m/s.

Formula

Speed = Distance ÷ Time

Worked Example

A cyclist covers 45 km in 1.5 hours. Their average speed is 45 ÷ 1.5 = 30 km/h. If the route was a winding trail rather than a straight line, this speed figure would still be 30 km/h, but their average velocity would differ, since velocity depends on straight-line displacement from start to end point, not total path distance.

Key Things to Know

  • Speed is a scalar; velocity is a vector: speed only has a magnitude, while velocity has both magnitude and direction.
  • A round trip has speed but zero average velocity: since net displacement is zero even though distance traveled is positive.
  • Instantaneous speed differs from average speed: a speedometer shows instantaneous speed at one moment, not the average across an entire journey.
  • Speed feeds into kinetic energy and momentum calculations, both of which technically use velocity, but speed is the magnitude component of that velocity.

Related Calculators

Speed Calculator →Calculate speed from distance and time instantly. Enter values in km, miles, or meters to get results in km/h, mph, and m/s all at once and free.
Velocity Calculator →Calculate velocity from displacement and time, with direction shown instantly. Unlike speed, velocity is a vector with signed displacement input.

Related Terms

VelocityVelocity (Physics)AccelerationAcceleration (Physics)

Frequently Asked Questions

What's the difference between speed and velocity?

Speed is a scalar quantity (distance ÷ time) with magnitude only, while velocity is a vector quantity (displacement ÷ time) that also includes direction. A runner completing a lap and returning to the starting point has a positive average speed but zero average velocity, since their net displacement is zero.

What's the difference between average speed and instantaneous speed?

Average speed is total distance traveled divided by total time elapsed over an entire trip, while instantaneous speed is how fast an object is moving at one specific moment, such as a speedometer reading. A car's average speed over a trip with stops can be much lower than its instantaneous speed while actually moving on the highway.

How do you convert speed between different units?

To convert km/h to m/s, divide by 3.6 (or multiply by 1000 and divide by 3600). To convert mph to km/h, multiply by approximately 1.609. The [Speed Calculator](/speed-calculator/) handles unit selection directly so you don't need to convert manually.

Can speed ever be negative?

No, speed is always zero or positive, since it's calculated from total distance traveled (which cannot be negative) divided by time. Velocity, by contrast, can be negative, since it reflects direction along a defined axis (such as moving backward relative to a starting point).