Mass and weight are related but different. This guide covers definitions, units, conversion, measurement, applications, and tips.
What's the Difference Between Mass and Weight?
Mass
- Amount of matter
- kg or g
- Constant everywhere
- Scalar (magnitude)
Weight
- Force due to gravity
- N or lbf
- Varies with location
- Vector (magnitude+direction)
Key Concept:
W = m×g. On Earth g ≈ 9.81 m/s² → 1 kg weighs ≈ 9.81 N; mass is invariant.
Units of Mass and Weight
Mass Units
- kg (SI)
- g = 0.001 kg
- t = 1000 kg
- lbm = 0.4536 kg
- oz = 28.35 g
Weight Units
- N (kg·m/s²)
- lbf = 4.448 N
- kgf = 9.807 N
- dyn = 1e‑5 N
Mass and Weight Conversion Table
| Unit | Kilograms (kg) | Pounds (lb) | Ounces (oz) | Newtons (N) on Earth |
|---|---|---|---|---|
| 1 kg | 1 | 2.2046 | 35.274 | 9.807 |
| 1 lb | 0.4536 | 1 | 16 | 4.448 |
| 1 oz | 0.0283 | 0.0625 | 1 | 0.278 |
| 1 N | 0.102 | 0.2248 | 3.6 | 1 |
Measuring Mass and Weight
Balance scales
Compare unknown mass to standards.
Spring scales
Weight from spring extension.
Load cells
Force → electrical signal (industrial).
Applications of Mass and Weight
Commerce
- Weigh goods
- Shipping
- Jewelry
- Portion control
Health
- Body weight
- Dosages
- Nutrition
- Lab work
Industry
- Manufacturing
- Quality control
- Material handling
- Packaging
Science
- Reactions
- Experiments
- Astronomy
- Density
Did You Know?
Since 2019, the kilogram is defined via the Planck constant (no physical artifact).
Mass and Weight in Everyday Life
Common weights
- Paperclip ~1 g
- Phone ~170 g
- 1 L water ~1 kg
- Adult ~62 kg
- Elephant ~5,000 kg
On other bodies (70 kg person)
- Sun 19,306 N
- Jupiter 1,818 N
- Earth 687 N
- Mars 260 N
- Moon 113 N
- Pluto 41 N
Practical Tip:
Baking is more accurate by weight (g/oz) than by volume (cups). Use a kitchen scale.