Key Concepts: SI System & Prefixes

The International System of Units (SI)

The SI system is the globally adopted standard for scientific measurement. It defines seven base units from which all other units are derived.

• Meter (m) — length
• Kilogram (kg) — mass
• Second (s) — time
• Ampere (A) — electric current
• Kelvin (K) — temperature
• Mole (mol) — amount of substance
• Candela (cd) — luminous intensity

SI Prefixes

Prefixes scale units by powers of 10 for convenience:

• Giga (G) = 10⁹, Mega (M) = 10⁶, Kilo (k) = 10³
• Centi (c) = 10⁻², Milli (m) = 10⁻³, Micro (μ) = 10⁻⁶, Nano (n) = 10⁻⁹

Example: 5.2 km = 5.2 × 10³ m = 5200 m