What Is the Difference Between Weight and Mass?

Mass vs Weight: Comparing and Understanding the Differences

A series of grey metal weights on a white background

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The terms "mass" and "weight" are used interchangeably in ordinary conversation, but the two words don't mean the same thing. The difference between mass and weight is that mass is the amount of matter in a material, while weight is a measure of how the force of gravity acts upon that mass.

  • Mass is the measure of the amount of matter in a body. Mass is denoted using m or M.
  • Weight is the measure of the amount of force acting on a mass due to the acceleration due to gravity. Weight usually is denoted by W. Weight is mass multiplied by the acceleration of gravity (g).

W=mgW = m * gW=mgComparing Mass and Weight

For the most part, when comparing mass and weight on Earth—without moving!—the values for mass and weight are the same. If you change your location with respect to gravity, mass will remain unchanged, but weight will not. For example, your body's mass is a set value, but your weight is different on the Moon compared with on Earth.

Mass is a property of matter. The mass of an object is the same everywhere. Weight depends on the effect of gravity. Weight increases or decreases with higher or lower gravity.
Mass can never be zero. Weight can be zero if no gravity acts upon an object, as in space.
Mass does not change according to location. Weight varies according to location.
Mass is a scalar quantity. It has magnitude. Weight is a vector quantity. It has magnitude and is directed toward the center of the Earth or other gravity well.
Mass may be measured using an ordinary balance. Weight is measured using a spring balance.
Mass usually is measured in grams and kilograms. Weight often is measured in newtons, a unit of force.

How Much Do You Weigh on Other Planets?

While a person's mass doesn't change elsewhere in the solar system, the acceleration due to gravity and weight varies dramatically. The calculation of gravity on other bodies, as on Earth, depends not just on mass but also on how far the "surface" is from the center of gravity. On Earth, for example, your weight is slightly lower on a mountain top than at sea level. The effect becomes even more dramatic for large bodies, such as Jupiter. While the gravity exerted by Jupiter due to its mass is 316 times greater than that of Earth, you wouldn't weigh 316 times more because its "surface" (or the cloud level we call the surface) is so far out from the center.

Other celestial bodies have different values of gravity than Earth does. To get your weight, simply multiply by the appropriate number. For example, a 150-pound person would weigh 396 pounds on Jupiter, or 2.64 times their weight on Earth.

Body Multiple of Earth Gravity Surface Gravity (m/s2)
Sun 27.90 274.1
Mercury 0.3770 3.703
Venus 0.9032 8.872
Earth 1 (defined) 9.8226
Moon 0.165 1.625
Mars 0.3895 3.728
Jupiter 2.640 25.93
Saturn 1.139 11.19
Uranus 0.917 9.01
Neptune 1.148 11.28

You may be surprised by your weight on other planets. It makes sense that a person would weigh about the same on Venus, because that planet is about the same size and mass as Earth. However, it may seem odd that you'd actually weigh less on the gas giant Uranus. Your weight would be only slightly higher on Saturn or Neptune. Although Mercury is much smaller than Mars, your weight would be about the same. The Sun is much more massive than any other body, yet you'd "only" weigh about 28 times more. Of course, you'd die on the Sun from the massive heat and other radiation, but even if it were cold, the intense gravity on a planet that size would be deadly.

Resources and Further Reading

  • Galili, Igal. “Weight versus Gravitational Force: Historical and Educational Perspectives.” International Journal of Science Education, vol. 23, no. 10, 2001, pp. 1073-1093.
  • Gat, Uri. “The Weight of Mass and the Mess of Weight.” Standardization of Technical Terminology: Principles and Practice, edited by Richard Alan Strehlow, vol. 2, ASTM, 1988, pp. 45-48.
  • Hodgman, Charles D., editor. Handbook of Chemistry and Physics. 44th ed., Chemical Rubber Co, 1961, pp. 3480-3485.​
  • Knight, Randall Dewey. Physics for Scientists and Engineers: a Strategic Approach. Pearson, 2004, pp 100-101.
  • Morrison, Richard C. “Weight and Gravity—The Need for Consistent Definitions.” The Physics Teacher, vol. 37, no. 1, 1999.