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Voltage Converter
Convert volts, millivolts and kilovolts, and check mains voltage before you travel.
Plug a US 120V hairdryer into a UK 230V socket without a proper converter and, at best, nothing happens. At worst, you hear a pop and smell something burning. The plug shape is the obvious problem; the voltage mismatch is the one that actually damages the appliance.
Mains voltage by region
| Region | Typical voltage | Frequency |
|---|---|---|
| United States, Canada | 120V | 60 Hz |
| United Kingdom, EU | 230V | 50 Hz |
| Japan (east, incl. Tokyo) | 100V | 50 Hz |
| Japan (west, incl. Osaka) | 100V | 60 Hz |
| Australia | 230V | 50 Hz |
Why Japan runs two different frequencies
Japan is the oddest case on the list, and the reason is historical rather than technical. In the 1890s, Tokyo bought its first generators from the German company AEG, which built 50 Hz equipment, while Osaka bought from the American General Electric, which built 60 Hz equipment. Neither city switched afterward, so Japan still runs a 50 Hz eastern grid and a 60 Hz western grid split roughly down the middle of the country, with converter stations linking the two.
The US settled on 120V partly because of Thomas Edison’s early direct-current systems, which ran incandescent bulbs at around 110V as a balance between bulb lifespan and wiring cost. As AC won out over DC in the “War of the Currents,” the voltage figure carried over largely unchanged, and 120V nominal is what stuck in North America.
Reading a voltage figure correctly
- Volt (V) — the base unit, one joule of energy per coulomb of charge.
- Millivolt (mV) — one thousandth of a volt, used for small signals like sensor outputs and biological measurements such as an ECG.
- Kilovolt (kV) — one thousand volts, used for power transmission lines and high-voltage equipment.
- Nominal voltage — the standard rated figure (like 230V); actual mains voltage typically drifts within about ±10% of it.
Before you plug an appliance in abroad
- Check the appliance’s label for its rated voltage, usually printed near the power cable.
- Check whether it says a single figure (like 120V) or a range (like 100–240V) — a ranged rating is dual-voltage and needs only a plug adapter.
- If it lists a single voltage that does not match your destination, you need an actual voltage converter, not just a plug adapter.
- Check the wattage too; small step-down converters are often rated for a maximum load and can overheat above it.
Voltage conversion questions
What is the difference between a plug adapter and a voltage converter?
A plug adapter only changes the shape of the plug so it fits a foreign socket; it does nothing to the electricity itself. A voltage converter actually changes the voltage, which is what you need if an appliance is not rated for the local mains voltage.
Can I plug a 120V US appliance into a 230V UK socket with just an adapter?
Only if the appliance is explicitly dual-voltage, usually shown as a range like 100–240V on its label. A single-voltage 120V appliance plugged into 230V without a real converter can be damaged or become a fire risk.
How many volts are in a kilovolt?
1,000. Power transmission lines commonly run at tens or hundreds of kilovolts specifically to reduce current, and therefore energy loss, over long distances, stepping back down to a few hundred volts near your home.
Why does Japan use two different electrical frequencies?
A historical accident: Tokyo imported German 50 Hz generators and Osaka imported American 60 Hz generators in the 1890s, and neither region ever converted to match the other. The country still runs a split grid today.
Is higher mains voltage more dangerous?
Generally yes, all else being equal, since higher voltage drives more current through a given resistance, including the human body. That said, both 120V and 230V mains supplies are capable of causing fatal electric shock, so neither should be treated as the safe one.
