Weight

Weight is the force exerted on an object due to gravity. Unlike mass, which is an intrinsic property of matter, weight depends on the gravitational field in which the object is located. Weight is calculated using the formula:

weight = mass × gravitational acceleration or W = mg,

where W is weight (a force), m is mass, and g is the acceleration due to gravity. On Earth, g is approximately 9.81 m/s² in SI units or 32.174 ft/s² in U.S. Customary units.

Since weight is a force, its units match those of force:

  • In the SI system, weight is measured in newtons (N), where 1 N = 1 kg·m/s².
  • In the U.S. Customary system, weight is measured in pounds-force (lbf), which represents the force exerted by Earth’s gravity on a 1-pound mass (lbm).

Because weight depends on gravity, it varies with location—for example, an object weighs less on the Moon than on Earth. However, its mass remains the same. This distinction is important in engineering and physics, particularly in aerospace applications where gravitational differences affect forces acting on structures and materials.