Physics overview
What is weight?
Weight is the gravitational force acting on an object. It depends on both the object's mass and the local gravitational acceleration.
An object keeps the same mass when moved between planets or moons, but its weight changes because gravitational acceleration is different.
Formula
Weight formula
WeightW = m × g
- W is weight in newtons.
- m is mass in kilograms.
- g is gravitational acceleration in meters per second squared.
Worked example
Calculate the weight of a 10 kg object on Earth
- Write the formula: W = m × g.
- Substitute the values: W = 10 × 9.80665.
- Calculate the result: W = 98.0665 N.
Gravity comparison
Calculate weight on the Moon
A 60 kg person has a mass of 60 kg on both Earth and the Moon. Using lunar gravity of approximately 1.62 m/s²:
Lunar weightW = 60 × 1.62 = 97.2 N
The person's mass remains 60 kg, but the gravitational force acting on that mass is much smaller.
Rearranged equations
Solve for mass or gravity
Mass
m = W ÷ g
Divide weight by gravitational acceleration.
Gravity
g = W ÷ m
Divide weight by a positive mass.
Important distinction
Mass is not the same as weight
Mass
Measured in kilograms
Mass describes the amount of matter in an object and does not depend on location.
Weight
Measured in newtons
Weight is a force and changes when gravitational acceleration changes.
Standard gravity
Which Earth gravity value should you use?
Standard gravitational acceleration is defined as 9.80665 m/s². Many school and laboratory problems round this value to 9.81 m/s² or 9.8 m/s².
Use the precision requested by your assignment or experiment. Do not round intermediate results too early when a precise final answer is required.
Relationship to force
Weight is a specific type of force
Newton's second law states that force equals mass multiplied by acceleration. For weight calculations, the acceleration is specifically gravitational acceleration.
General forceF = m × a
Gravitational forceW = m × g
Units
Use consistent SI units
- Enter mass in kilograms.
- Enter gravity in meters per second squared.
- Report weight in newtons.
- Convert grams to kilograms before calculating.
One newton1 N = 1 kg·m/s²
Assumptions
What the calculation represents
- Mass and gravity must be greater than zero.
- Gravity is treated as constant for the calculation.
- The calculator uses SI units without automatic unit conversion.
- The result represents gravitational force, not apparent weight caused by additional acceleration.
Related tools
Continue your gravity calculations
Use the Force Calculator to calculate general force, mass, or acceleration using Newton's second law.
Use the Acceleration Due to Gravity Calculator to estimate gravity from a celestial body's mass and radius.
Use the Gravitational Potential Energy Calculator to calculate energy from mass, gravity, and height.
Questions and answers
Weight calculator FAQ
What formula does the weight calculator use?
The calculator uses W = m × g, where W is weight in newtons, m is mass in kilograms, and g is gravitational acceleration in meters per second squared.
What is the difference between mass and weight?
Mass measures the amount of matter in an object and remains constant, while weight is the gravitational force acting on that mass and changes when gravity changes.
What value should I use for gravity on Earth?
Standard Earth gravity is 9.80665 meters per second squared. For many classroom calculations, 9.81 meters per second squared is sufficiently precise.
Does an object's mass change on the Moon?
No. Mass remains the same, but weight decreases because the Moon's gravitational acceleration is much lower than Earth's.
Is weight measured in kilograms or newtons?
In physics, weight is a force and is measured in newtons. Kilograms measure mass, not weight.