Voltage is the difference in electric potential between two points — the "pressure" that pushes current through a circuit. The SI unit is the volt, but the useful range spans twelve orders of magnitude, from the microvolts a thermocouple produces to the megavolts on a transmission line. That is why converting between prefixes comes up constantly in electronics work: a datasheet quotes an offset in millivolts, your meter reads in volts, and the spec you are checking against is written in a third unit.
Every conversion here is a decimal shift. Voltage prefixes are pure powers of ten, so there is no awkward constant to remember and no rounding error introduced by the conversion itself — only by the precision of your original measurement.
Voltage prefix reference
| Unit | Symbol | In volts | Typically seen in |
|---|---|---|---|
| Microvolt | µV | 0.000001 V | Thermocouples, EEG and ECG signals, antenna inputs |
| Millivolt | mV | 0.001 V | Sensor outputs, op-amp offsets, shunt measurements |
| Volt | V | 1 V | Batteries, logic levels, mains-powered electronics |
| Kilovolt | kV | 1,000 V | X-ray tubes, ignition systems, distribution lines |
| Megavolt | MV | 1,000,000 V | High-voltage transmission, lightning research |
Voltages worth knowing by heart
- AA alkaline cell: 1.5 V nominal, dropping toward 1.0 V as it discharges.
- Lithium-ion cell: 3.7 V nominal, 4.2 V fully charged, 3.0 V considered empty.
- USB bus power: 5 V, with USB Power Delivery negotiating 9 V, 15 V or 20 V.
- Logic families: 3.3 V and 5 V dominate, with modern low-power parts at 1.8 V.
- Mains supply: 120 V in North America, 230 V across most of Europe and Asia.
- Car electrical system: 12 V nominal, around 14.4 V with the alternator running.
Where voltage fits with current, resistance and power
Ohm's law ties three of these together: V = I × R. A volt across one ohm drives one amp. Power follows from P = V × I, which is why doubling the transmission voltage lets you carry the same power at half the current — and, because resistive loss is I²R, at a quarter of the loss. That single relationship is the reason long-distance power lines run at hundreds of kilovolts rather than at the voltage anyone actually uses.
When you convert a reading, keep the significant figures your instrument actually gave you. A meter showing 3.30 V has told you three significant figures; writing the result as 3,300,000.000 µV implies a precision the measurement never had.
A note on safety
Voltage alone does not describe danger — current through the body does, and that depends on voltage, skin resistance and path. As a rough working line, anything above about 50 V AC or 120 V DC is treated as hazardous by most electrical standards. Static discharge can reach tens of kilovolts and merely stings because the energy behind it is tiny; mains at 230 V can be lethal because it can sustain current. Convert units freely, but do not read a small number in kilovolts as a small risk.
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