Voltage Converter

Voltage is the difference in electrical potential between two points, the push that drives current through a circuit. The usual analogy is water pressure: voltage is the pressure, current is the flow. The SI unit is the volt (V), and it covers an enormous range in ordinary life.

Metric prefixes:

• 1 V = 1,000 mV (millivolts)
• 1 kV = 1,000 V (kilovolts)
• 1 MV = 1,000,000 V (megavolts)

Voltages you meet:

• AA battery: 1.5 V
• USB charging: 5 V
• US household outlet: 120 V
• EU household outlet: 230 V
• High-voltage transmission line: 110 to 765 kV

Voltage is what decides whether current can force its way through a given resistance, including you. Dry skin blocks current well at low voltage, which is why a 9 V battery on your tongue tingles but the same battery in your hand does nothing. At hundreds of volts that protection breaks down and current flows freely, which is the real hazard of mains and transmission lines.

One subtlety worth carrying around: an AC voltage has two numbers. The “120 V” or “230 V” on your outlet is the RMS value, the effective figure used for power. The actual peak swings about 1.41 times higher, near 170 V or 325 V. Insulation and components have to survive the peak, not the RMS, so that distinction is more than academic.

Where each prefix actually turns up

Millivolts are the language of sensors and signals. A thermocouple puts out tens of microvolts per degree, an ECG trace is about one millivolt, and a moving-coil phono cartridge delivers a fraction of a millivolt, which is why those inputs need so much amplification and pick up so much hum.

Volts cover almost everything you handle: batteries from 1.2 to 12, USB at 5, mains at 120 or 230, an electric car pack at 400 or 800.

Kilovolts start at the neon sign and the old CRT television, run through the 11 kV and 33 kV distribution lines on wooden poles, and reach the 400 kV steel pylons that carry power between cities. Megavolts belong to lightning and to laboratory equipment, and essentially nothing else.

A useful check on any voltage figure is the prefix itself. A datasheet quoting an offset in millivolts and a supply in volts is normal; one quoting both in the same unit usually means somebody dropped a prefix in a spreadsheet, and the error is a factor of a thousand rather than a small one.