Measurement
The Metric System - Measurement Built on Tens
The metric system is the world's most widely used system of measurement. Built on a foundation of ten, it makes converting between units simple and logical. Scientists, engineers, and most countries worldwide use it as the standard.
Today, only three countries – the United States, Liberia, and Myanmar – have not officially adopted the metric system as their primary measurement standard, making it very nearly universal worldwide. The cost of mixing systems became a famous, expensive lesson in 1999, when NASA lost the $125 million Mars Climate Orbiter spacecraft because one engineering team calculated a thruster force using metric newton-seconds while another team's software expected the imperial pound-force-seconds – the tiny mismatch built up over the months-long journey to Mars and sent the spacecraft too close to the planet, destroying it. It remains one of the most cited examples of why scientists and engineers insist on using one consistent system of units throughout an entire project.
What Is the Metric System?
The metric system (formally the International System of Units, SI) uses seven base units. All other units are derived from these. The power of the metric system lies in its prefixes – each one represents a power of ten.
The Seven SI Base Units
| Quantity | Unit | Symbol |
|---|---|---|
| Length | Metre | m |
| Mass | Kilogram | kg |
| Time | Second | s |
| Temperature | Kelvin | K |
| Electric current | Ampere | A |
| Amount of substance | Mole | mol |
| Luminous intensity | Candela | cd |
Metric Prefixes
| Prefix | Symbol | Meaning | Example |
|---|---|---|---|
| Tera | T | 10¹² | 1 TB = 10¹² bytes |
| Giga | G | 10&sup9; | 1 GHz = 10&sup9; Hz |
| Mega | M | 10&sup6; | 1 MW = 10&sup6; W |
| Kilo | k | 10³ | 1 km = 1,000 m |
| Hecto | h | 10² | 1 hm = 100 m |
| Deca | da | 10¹ | 1 dam = 10 m |
| (Base unit) | — | 10&sup0; = 1 | metre, gram, litre |
| Deci | d | 10−¹ | 1 dm = 0.1 m |
| Centi | c | 10−² | 1 cm = 0.01 m |
| Milli | m | 10−³ | 1 mm = 0.001 m |
| Micro | µ | 10−&sup6; | 1 µm = 0.000001 m |
| Nano | n | 10−&sup9; | 1 nm = 10−&sup9; m |
Why the Metric System Is So Useful
- Every conversion is a multiple of 10 – just move the decimal point.
- The same prefixes apply to all quantities: kilogram, kilometre, kilolitre.
- It is consistent worldwide, reducing errors in science and trade.
Worked Examples
kilo = 10³, so × 1,000. 5.3 × 1,000 = 5,300 m.
milli = 10−³, so ÷ 1,000. 4,200 ÷ 1,000 = 4.2 l.
Key Takeaways
- The SI system has 7 base units; all other units are derived from them.
- Prefixes (kilo, centi, milli, etc.) each represent a power of 10.
- Converting in the metric system always means multiplying or dividing by a power of 10.