Momentum Calculator Solve for Mass Velocity and Momentum

Mass (m)	--
Velocity (v)	--
Momentum (p)	--
Kinetic Energy (K)	--

Last Updated: June 30, 2026

What is Momentum?

Momentum is a measure of how much motion an object has, based on both its mass and its velocity. A heavy truck moving slowly and a small car moving fast can have similar momentum, even though they look nothing alike. That is the core idea behind this concept: motion alone does not tell the full story, and neither does mass alone. The two have to be considered together.

Momentum is a vector quantity, which means it has both magnitude and direction. An object moving forward has momentum in the forward direction. If it reverses, its momentum reverses too, even if its speed stays the same.

Use our momentum calculator above to find momentum, mass, or velocity by entering any two known values. The tool automatically converts between units and calculates the third value for you.

Momentum Calculator Formula and Calculation

The formula for momentum is one of the simplest in physics.

p = m \times v

Where p is momentum, m is mass, and v is velocity. Momentum is measured in kilogram meters per second (kg·m/s), which is the same as a newton-second (N·s).

Example finding momentum: A 5 kg object is moving at 12 m/s. What is its momentum?

\begin{aligned} p &= m \times v \\ &= 5 \times 12 \\ &= 60\ \text{kg}\cdot\text{m/s} \end{aligned}

momentum calculator with mass and velocity values entered to solve for momentum

momentum calculator result showing physics breakdown and step by step solution

Rearranging the formula

Since the calculator can solve for any of the three variables, it relies on two rearranged versions of the same formula.

To find mass when you know momentum and velocity:

m = \frac{p}{v}

Example finding mass: An object has a momentum of 60 kg·m/s and is moving at 12 m/s. What is its mass?

\begin{aligned} m &= \frac{p}{v} \\ &= \frac{60}{12} \\ &= 5\ \text{kg} \end{aligned}

To find velocity when you know momentum and mass:

v = \frac{p}{m}

Example finding velocity: An object with a mass of 5 kg has a momentum of 60 kg·m/s. What is its velocity?

\begin{aligned} v &= \frac{p}{m} \\ &= \frac{60}{5} \\ &= 12\ \text{m/s} \end{aligned}

Each of these can be solved directly in the calculator above by entering any two of the three numbers shown.

How to Use This Momentum Calculator

This calculator is built to solve for whichever value you are missing, so there is no need to pick a mode first.

Enter any two of the three values: mass, velocity, or momentum
Select the correct unit for each value you enter from the dropdown next to it
The third field calculates automatically as soon as two values are filled in, with no need to click a separate button
The result panel shows your answer along with the full physics breakdown, including kinetic energy, and a step-by-step explanation of how the formula was applied

If you change a unit after calculating, the result updates instantly to reflect the new conversion. This means you can compare the same scenario across different unit systems, such as switching from kilograms to pounds, without retyping any values.

Momentum vs Kinetic Energy: What is the Difference?

Momentum and kinetic energy are both related to motion, but they are not the same quantity, and students frequently mix them up.

Momentum is p = mv. It scales directly with velocity. Double the velocity and momentum doubles too.

Kinetic energy is KE = ½mv². It scales with the square of velocity. Double the velocity and kinetic energy quadruples.

This difference matters in real situations. A car going twice as fast does not just have twice the stopping difficulty, it has roughly four times the kinetic energy to dissipate, which is part of why braking distances increase so sharply at higher speeds. Momentum, meanwhile, behaves more predictably and is the quantity that is always conserved in a collision, which is why it is the variable used in collision and impulse problems.

Our calculator shows both values side by side in the results breakdown, so you can see how they relate for the same object.

What is the unit of momentum?

The SI unit of momentum is kilogram meters per second (kg·m/s), which is equivalent to a newton-second (N·s). Our calculator also supports imperial units like pound-feet per second.

Can this calculator handle different unit systems at the same time?

Yes. You can enter mass in pounds and velocity in kilometers per hour, and the calculator converts everything to SI units internally before solving, then converts the result back to whichever output unit you select.

What happens to momentum in a collision?

In a closed system with no external forces, total momentum before a collision equals total momentum after the collision. This is the law of conservation of momentum, and it holds true whether the collision is elastic or inelastic.

Is momentum the same as force?

No. Force is mass times acceleration (F = ma), while momentum is mass times velocity (p = mv). They are related through impulse, which equals the change in momentum, but they measure different things and use different units.