The SI System

Base units and prefixes

An interactive lesson with 7 steps, about 6 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• SI has seven base units: m, kg, s, A, K, mol, cd.
• Every other unit is a combination of them, such as N = kg·m/s².
• Prefixes: n (10⁻⁹), µ (10⁻⁶), m (10⁻³), k (10³), M (10⁶), G (10⁹).

Steps

1. A costly mix-up
2. Seven base units
3. Prefixes
4. Read a prefix
5. Small masses
6. Building units
7. Tiny times