Convert between milli, kilo, mega and other prefixes by moving the decimal, and tell dB from the power ratio.
Syllabus: Math for electronics: conversion of electrical units, decibels
Compendium articles on the ideas in this lesson, beyond what the exam asks.
Practise the 13 pool questions for this group. Answers are shuffled, and every one comes with a one-line "why".
A prefix in front of a unit says how many of that unit you have.
| Prefix | Symbol | Means |
|---|---|---|
| giga | G | 1,000,000,000 (a thousand million) |
| mega | M | 1,000,000 (a million) |
| kilo | k | 1,000 (a thousand) |
| (none) | 1 | |
| milli | m | one thousandth (0.001) |
| micro | µ | one millionth (0.000001) |
| nano | n | one billionth |
| pico | p | one trillionth |
RememberKilo = ×1,000. Micro = ÷1,000,000. Each step in the table is ×1000.
A smaller unit means you need more of them, so the number gets bigger. A bigger unit means a smaller number.
| Convert | Move | Result |
|---|---|---|
| 1.5 A → mA | smaller unit, ×1000 | 1500 mA |
| 1,500,000 Hz → kHz | bigger unit, ÷1000 | 1500 kHz |
| 3.525 MHz → kHz | smaller unit, ×1000 | 3525 kHz |
| 28,400 kHz → MHz | bigger unit, ÷1000 | 28.4 MHz |
| 1,000,000 pF → µF | 2 rungs bigger, ÷1,000,000 | 1 µF |
Memory hookSmaller unit, bigger number. Check the direction before you move the point.
A decibel (dB) compares two powers. Only the ratio matters. Every doubling is about +3 dB, every halving −3 dB, and ×10 is +10 dB.
| Change | Ratio | Decibels |
|---|---|---|
| 5 W → 10 W | ×2 | +3 dB |
| 12 W → 3 W | ÷2, ÷2 = ÷4 | −3 −3 = −6 dB |
| 20 W → 200 W | ×10 | +10 dB |
RememberRatios multiply, decibels add. Gain is positive, loss is negative.