A resistor might be 47 Ω or 4.7 MΩ. A capacitor might be 100 pF or 4700 µF. A current might be 2 A or 50 µA. The underlying units never change — only the prefix in front does. Getting the prefix wrong by one step is a factor of a thousand, which is why it is worth being systematic.
The prefixes that matter in electronics
Each step is a factor of 1000. Electronics uses these far more than the intermediate ones (centi-, deci-) that appear in everyday measurement.
| Prefix | Symbol | Multiplier |
|---|---|---|
| mega | M | 1 000 000 (10⁶) |
| kilo | k | 1 000 (10³) |
| — | — | 1 |
| milli | m | 0.001 (10⁻³) |
| micro | µ | 0.000 001 (10⁻⁶) |
| nano | n | 10⁻⁹ |
| pico | p | 10⁻¹² |
Two conventions catch people out. Capital M is mega; lowercase m is milli — they differ by a factor of a billion. And µ (the Greek letter mu) is often typed as “u” when a keyboard makes it awkward, so “uF” and “µF” mean the same thing.
Moving between prefixes
Converting is always the same operation: multiply or divide by a power of 1000.
Going down the table — from a large prefix to a smaller one — the number gets bigger:
1 A = 1 000 mA = 1 000 000 µAGoing up, the number gets smaller:
4 700 000 Ω = 4 700 kΩ = 4.7 MΩThe reliable method is to convert to the base unit first and then out again, rather than trying to jump two prefixes in one step. That is exactly how this site calculates: every value passes through the base unit — ohms, amperes, volts — before being expressed in the target. The general technique is covered in how to convert units.
Where each prefix actually shows up
Resistance spans the widest range. Pull-up resistors sit in kiloohms, current-sense resistors in milliohms, and insulation resistance is often quoted in megaohms or gigaohms. Convert with ohms to kiloohms or megaohms to ohms.
You will also see these written as kilohm, megohm and gigohm — the vowel is commonly elided in datasheets and standards. They mean the same thing; this site spells them out in full.
Current runs from amperes in power circuits down to microamperes in sleep-mode electronics — a battery-life calculation often hinges on the difference between 10 µA and 10 mA. See milliamperes to amperes.
Voltage is usually volts or millivolts at signal level, kilovolts in transmission and insulation testing. See kilovolts to volts.
Capacitance is almost never quoted in farads — a farad is enormous. Real components are microfarads, nanofarads and picofarads. See all capacitance units.
Inductance behaves similarly: henries are large, so millihenries and microhenries do the everyday work. See millihenries to henries.
Conductance is the reciprocal of resistance, measured in siemens, and shows up in sensor and water-quality work as microsiemens and millisiemens. See microsiemens to millisiemens.
Worked example
A datasheet gives a leakage current of 0.05 mA and you need it in microamperes.
- Start with the value in milliamperes: 0.05 mA.
- Milli and micro are one step apart, a factor of 1000.
- Going to the smaller prefix, multiply: 0.05 × 1000 = 50 µA.
The sanity check is direction: microamperes are smaller units, so the same quantity must be a bigger number. If your answer came out smaller, you divided when you should have multiplied.
A prefix warning specific to data units
Prefixes behave differently for digital storage. There, “kilo” has historically meant both 1000 and 1024 depending on context, which is why the separate binary prefixes — kibi, mebi, gibi — exist. Electrical units have no such ambiguity: kilo is always exactly 1000. The digital case is handled separately in the data storage converter.
Related reading
- The metric system — where SI prefixes come from
- Significant figures and precision — how many digits to keep
- Conversion methodology — how these values are calculated here