Velocity Calculator
Velocity describes how fast an object is moving and in what direction. This calculator supports two common velocity calculations. The first is average velocity from displacement and time: v = d / t, where d is displacement in metres and t is time in seconds. The second is the kinematic equation for constant acceleration: v = u + at, where u is initial velocity (m/s), a is acceleration (m/s²), and t is time (s). Results are shown in both metres per second (m/s) and kilometres per hour (km/h). Unlike speed, velocity is a vector quantity, meaning direction matters. The displacement formula uses net displacement rather than total distance, so an object that returns to its starting point has zero average velocity even if it travelled a large distance. The kinematic equation applies only under constant (uniform) acceleration. Select the calculation mode, enter the known values, and the result appears instantly. Uses include calculating a car's average speed on a trip, working out a ball's velocity under gravity, or checking kinematic motion problems.
Velocity: -- m/s (-- km/h)
Formulae
Average velocity: v = d / t
Kinematic: v = u + at
Unit conversion: km/h = m/s * 3.6
Worked examples
Average velocity: A car travels 500 m in 20 s.
- v = 500 / 20 = 25 m/s
- 25 * 3.6 = 90 km/h
Kinematic: A ball starts at rest (u = 0) and accelerates at 9.81 m/s² for 3 s.
- v = 0 + (9.81 * 3)
- v = 29.43 m/s = 105.95 km/h
Frequently asked questions
What is the difference between speed and velocity?
Speed is a scalar quantity: it has magnitude only (e.g., 60 km/h). Velocity is a vector quantity: it has both magnitude and direction (e.g., 60 km/h northward). In everyday speech the terms are often used interchangeably, but in physics they are distinct. Average speed is total distance divided by time; average velocity is displacement divided by time, where displacement is the straight-line change in position.
What does v = u + at mean?
This is one of the four kinematic equations for constant (uniform) acceleration. v is final velocity, u is initial velocity, a is acceleration, and t is time. The equation states that final velocity equals initial velocity plus the change in velocity (acceleration multiplied by time). It applies only when acceleration is constant throughout the motion.
How do I convert m/s to km/h?
Multiply metres per second by 3.6 to get kilometres per hour: km/h = m/s * 3.6. This is because 1 m/s = 3,600 m/h = 3.6 km/h. Going the other way, divide km/h by 3.6 to get m/s. For example, 30 m/s * 3.6 = 108 km/h.
What is displacement?
Displacement is the straight-line distance between the starting and ending positions of an object, measured in a specific direction. It differs from distance, which is the total path length travelled. If you walk 4 m east and then 3 m west, your distance is 7 m but your displacement is 1 m east. Displacement can be negative if the motion is in the negative direction.
Can velocity be zero if acceleration is not?
Yes. At the peak of a projectile's trajectory, the vertical component of velocity is momentarily zero while the vertical acceleration (due to gravity) is still 9.81 m/s² downward. Similarly, a ball thrown straight up has zero velocity at its highest point even though gravity continues to accelerate it downward.
Sources
- NIST SP 330 (2019): The International System of Units (SI).
- NIST Physics: Fundamental Physical Constants and SI Units.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. General information only.