Mass vs Weight: what's the difference?
GCSE Physics
Everyday speech treats these as the same, but in physics they are different quantities.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Mass vs Weight — side by side
| Mass | Weight | |
|---|---|---|
| What it is | The amount of matter in an object | The force of gravity on the object |
| Type | Scalar | Vector (a force) |
| Unit | kilograms (kg) | newtons (N) |
| Changes with location? | No — the same everywhere | Yes — depends on gravitational field strength (W = mg) |
Exam tip — how to tell them apart: Mass is measured in kg and never changes; weight is a force in newtons and changes with g (e.g. less on the Moon).
Common trap: Weighing scales in kg actually measure weight and convert — but in physics, weight is always in newtons.
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