The Language of Measurement
Units & Prefixes
10 min · 3 worked examples · 3 questionsFree
Why every number in engineering needs a unit, and how to move between milli, kilo and mega without slipping a factor of a thousand.
After this lesson you can
- Convert between milli, micro, kilo and mega without second-guessing yourself
- Spot when an answer is wrong by a factor of a thousand
- Know why m and M are not the same prefix
A number without a unit is meaningless
If someone tells you a resistor is "220", they have told you almost nothing. 220 ohms is a common LED resistor. 220 kilohms is a thousand times bigger and would leave your LED barely glowing. In engineering the unit carries as much information as the number, and writing it down every single time is a habit that prevents real damage.
The SI system gives us a base unit for each quantity: the volt (V) for voltage, the ampere (A) for current, the ohm (Ω) for resistance, the watt (W) for power, the second (s) for time. Everything else is built from these.
In the full lesson
- A number without a unit is meaningless
- Prefixes are just powers of ten
- Converting between prefixes
- Case matters
Free with an account. Read it, work the examples, answer the questions, then build it in the simulator.