Weight Calculator

About the Weight Calculator

A weight calculator computes the gravitational force (weight) acting on a mass using Newton's second law: W = m × g, where g is the local gravitational acceleration. On Earth at sea level, g = 9.80665 m/s² (standard gravity), giving weight in Newtons (N). The distinction between mass (kg, a measure of matter) and weight (N, a force) is fundamental in physics yet commonly confused in everyday language: people say they "weigh 70 kilograms," but technically they have a mass of 70 kg and a weight of 686 N. Mass is invariant; weight depends on gravity. This calculator enables comparisons of weight on different celestial bodies — a 70 kg person weighs 686 N on Earth, 114 N on the Moon (g = 1.62 m/s²), and 262 N on Mars (g = 3.72 m/s²). It also converts between N, lbf, and kgf. Useful for physics students studying Newton's laws, engineers specifying structural loads, aerospace engineers calculating launch mass, and anyone curious about their weight elsewhere in the solar system.

How It Works

W = m × g. Units: if mass is in kg and g in m/s², weight is in Newtons (N). 1 N = 1 kg·m/s². Conversion: 1 lbf (pound-force) = 4.44822 N; 1 kgf (kilogram-force) = 9.80665 N. Gravitational accelerations: Earth standard = 9.80665 m/s²; Moon = 1.6249 m/s² (1/6.048 Earth); Mars = 3.7210 m/s²; Jupiter = 24.790 m/s²; Saturn = 10.440 m/s²; Sun surface = 274.0 m/s². Example: 70 kg person. Earth: 70 × 9.807 = 686 N = 154.3 lbf. Moon: 70 × 1.625 = 113.8 N = 25.6 lbf. Mars: 70 × 3.721 = 260.5 N = 58.6 lbf. Jupiter: 70 × 24.79 = 1735 N = 390 lbf. Spring scale (weighing scale) measures weight force; balance (equal-arm) measures mass — a balance gives the same reading on the Moon.

Tips & Best Practices

• ✓Scales in shops and homes are calibrated to display mass (kg or lbs) assuming standard Earth gravity. When people say they "weigh 70 kg," they are using the colloquial meaning of weight as mass. In physics and engineering, weight strictly means force in Newtons.
• ✓Surface gravity varies slightly across Earth: it is highest at the poles (9.832 m/s²) due to Earth being slightly flattened and distance from the centre being smallest; lowest at the equator (9.780 m/s²) due to centrifugal force and greater distance. The standard 9.80665 m/s² is a defined constant, not an average.
• ✓Apparent weightlessness in orbit: astronauts in the International Space Station (400 km altitude) still experience about 90% of Earth's gravity. They feel weightless because they are in free fall — both they and the station fall at the same rate. True weightlessness only occurs far from all gravitational bodies.

Who Uses This Calculator

Physics students distinguishing mass from weight and performing calculations involving gravitational force. Engineers calculating structural loads, pressure on foundations, and forces on mechanical components. Space enthusiasts and students exploring how weight varies across planets and moons. Teachers demonstrating Newton's second law with practical numerical examples.