Mass vs. Weight – What’s the Difference?

The Mass of a body refers to the amount of matter it contains, whereas Weight is defined as the force which acts on a body due to acceleration due to gravity. Most people consider that both terms represent the same thing. However, Mass and Weight are pretty different from each other.

For students of Physics and other science fields, it is necessary to understand the critical differences between Mass and Weight. Students generally associate Mass and Weight with measuring how heavy an object is. It is a wrong approach to consider the same things.

What is Mass?

The Mass of a body is the measure of the substance it contains. The Mass of a body is a constant quantity. No one can destroy it. Mass is generally measured in Kilograms (Kg). It does not depend upon the body’s position, location, and shape.

As Mass measures the amount of substance it contains, we should know that matter consists of microscopic particles like Electrons, Protons, Neutrons, etc. Remember that the Mass of a body remains constant because the amount of matter in it remains constant. The Mass of a body changes when a substance decays or emits radiation. Hence the Mass of a substance decreases.

What is Weight?

The Weight of a substance is the force of gravity that acts on a body. The Weight of a body is a variable quantity. Weight changes as the position of a body changes. The Weight of a body can be measured by multiplying its mass(m) mass with the acceleration due to gravity(g) as; W=mg.

As Weight is a form of force, it is measured in newtons (N). When we lift a body from the ground, its Mass remains constant, but the gravitational acceleration changes, so the Weight of the body changes. The Weight of every object in space becomes zero; therefore, the things in a vacuum appear like free-floating objects.

Key Differences

  • Mass is the amount of matter in a body, while Weight is the force on a body due to gravitational acceleration.
  • Mass is measured in Kg, while Weight is always measured in newtons.
  • The body’s Mass is position dependent, while the body’s Weight depends on the height from sea level.
  • Mass is denoted by ‘M’ whereas Weight is meant by ‘W.’
  • Mass is a constant quantity, while Weight is a variable quantity.
  • Mass is measured as M= (density)(volume), while Weight can be inferred using the formula F=mg.
  • Mass is a scalar quantity, while Weight is a vector quantity.

Comparison Chart between Mass and Weight

Classification Mass Weight
Definition The measure of substance in a body The measure of force on a body due to gravitational acceleration
Units Kilograms Newton
Denoted by  ‘M’  ‘W’ or ‘F’
Variability Constant all time Changes with height
Quantity Scalar Vector


In a nutshell, we can say that Mass and Weight are different entities. They are different from each other in various aspects. Understanding the differences between Mass and Weight is necessary to clarify the other physics concepts.