Travel power guide
What Does "100–240V" Mean? (Dual Voltage Explained)
Direct answer
What Does "100–240V" Mean? (Dual Voltage Explained)
An input rating of 100-240V covers nominal voltages within that range. Confirm the frequency, plug, grounding and exact model instructions separately; the range is not permission to use every outlet.
Updated 2026-09-04
Most modern chargers — phones, laptops, cameras, tablets, most CPAP machines — are dual voltage. The label reads something like "INPUT 100–240V~ 50/60Hz".
You'll find the rating on the device, its plug, or its power brick. The voltage range is the part that matters for safety.
If the label shows only a single value such as "120V" or "220–240V", the device is single voltage and is not safe to plug into a different voltage without a converter.
Do not confuse input with output. A USB-C charger may say "65W" or "20V output"; the travel-safety line is still the AC INPUT rating, usually printed near the pins or on the power brick.
How to read the label, word by word
A typical charger label reads "INPUT: 100-240V~ 50/60Hz 0.5A". INPUT is the wall side — the only line that decides travel safety. The "~" symbol means alternating current, the kind every household grid supplies. "100-240V" is the range of grid voltages the device accepts, and "50/60Hz" means it accepts both of the world's grid frequencies.
The number after the frequency (for example "0.5A") is how much current the device draws at most. It matters for choosing a power strip or adapter current limit, not for the voltage question.
Labels hide in predictable places: molded into the plastic of a power brick, printed on the face of the plug between the pins, on the underside of an appliance, or inside a battery compartment. If the printing is worn away, check the manual or the manufacturer's specification page for the exact model number.
A range is not the same as two values
A continuous range like "100-240V" means the device adapts to anything in between on its own — nothing to configure. That is true dual voltage.
A pair of discrete values like "115/230V" usually marks a switchable device: somewhere on the housing there is a small selector, often recessed and red. It must be set to match the destination grid before you plug in. On a 230V grid with the switch left at 115V, the device receives roughly double the voltage it expects — the classic burnout.
A single value like "120V" or "230V" is single voltage. On a different grid it needs a correctly sized voltage converter, or it stays home.
What is usually dual voltage — and what almost never is
Usually dual voltage: phone, tablet and laptop chargers, camera battery chargers, USB power bricks, e-reader chargers, and most electric shaver charging bases. These are switch-mode power supplies, and 100-240V input has been the industry norm for years.
Almost never dual voltage: hair dryers, curling irons, flat irons, kettles, and clothes irons sold for the home market. Heating elements are built for one voltage, and the high wattage that makes them useful also makes a converter impractical. Dual-voltage travel versions of these tools exist — they are the deliberate exception, and their label still has to say so.
Label-dependent: CPAP machines and other devices with external power supplies often ship with 100-240V bricks, but the only proof is the printed rating on your unit. PlugVoltage's verdict for these devices is deliberately "check the label", never an assumption.
Even a genuine dual-voltage rating only settles voltage. Devices with AC motors or clocks can still run at a different speed on a 50Hz grid versus 60Hz — see the frequency note below.
Frequency: what 50/60Hz does and does not cover
Most dual-voltage electronics also accept both grid frequencies — that is what the "50/60Hz" on the label declares — so chargers and power bricks travel without a second thought.
Frequency still matters for devices that use the grid's rhythm directly: simple AC motors can spin faster or slower, and old clock radios or appliance timers that count grid cycles drift on the wrong frequency.
No plug adapter and no ordinary voltage converter changes frequency. If a motorized device is frequency-sensitive, the practical answer is a version built for the destination, not more gear.
No label? Treat it as single voltage
If you cannot find any input rating, the safe assumption is that the device is single voltage for the market it was sold in. That is also how the PlugVoltage checker fails: when data is uncertain, the verdict is "check the label", never "it will probably work".
Before the trip, look up the exact model on the manufacturer's site, or photograph the label of every device you pack — a camera roll of labels answers most airport doubts in seconds.
What the evidence covers
A source supports only the facts, socket types or models listed below. A model example does not verify every device in its category. Confirm your own label and outlet.
- Apple: MacBook Pro USB-C power adapter specifications · checked: 2026-08-21
Apple lists 100–240V AC, 50–60Hz for the named 70W, 96W and 140W USB-C power adapters. Power adapter specifications. A checked manufacturer family example; not proof for every USB, GaN or laptop charger.
- Kansai Electric: Voltage and frequency in Japan · checked: 2026-09-04
Standard supply is 100V; eastern and western areas use 50Hz and 60Hz respectively. Some appliances use distinct 200V sockets. Voltage and frequency sections and regional map. The utility advises checking the manual or manufacturer. A country average does not establish a specific outlet or appliance rating.
- ResMed: AirSense 11 user guide · checked: 2026-08-21
The AirSense 11 65W supply specifies 100–240V, 50–60Hz; typical and peak consumption differ. Technical specifications, printed page 22 (PDF page 25). Only the named supply and machine are covered. Confirm your own supply, accessories and manufacturer instructions.
Dual-voltage labels that are safe to recognize
Look for the AC input range, not the USB output or brand name.
Label examples to recognize
Use these text patterns as visual cues before you trust a charger, hair tool, or adapter abroad.
Frequently asked questions
How do I know if my device is dual voltage?
Find the INPUT line on the device, its plug, or its power brick. A range that spans both voltage worlds — "100-240V" — means dual voltage. A single value like "120V" means single voltage.
Is 120V dual voltage?
No. "120V" alone is a single-voltage rating. Dual voltage requires a printed range that covers both the 100-127V and the 220-240V grid families, such as "100-240V".
Are all USB chargers dual voltage?
Almost all modern, brand-name USB chargers are rated 100-240V, but the rating on your specific brick is the only proof. Very old, counterfeit, or bundled no-name units are the usual exceptions.
Does dual voltage mean I can plug in anywhere without an adapter?
No. Dual voltage solves the voltage question only. If the destination uses a different socket shape, you still need a plug adapter — it changes the shape, never the voltage.
What does "INPUT 100-240V~ 50/60Hz" mean exactly?
The device accepts any household AC grid from 100 to 240 volts at either 50 or 60 hertz — effectively every standard outlet in the world, with at most a plug adapter for the socket shape.
My label says 110-220V. Is that dual voltage too?
It spans two voltage families, but the exact range still excludes Japan at 100V and a 230-240V grid. The checker returns Check Label outside the printed range. Do not widen a rating based on a voltage family.
Do I need to flip a switch on a 115/230V device?
Yes. Dual-value devices with a voltage selector must be set to the destination voltage before plugging in. A selector left on 115V in a 230V country can destroy the device.
Is dual voltage the same as using a voltage converter?
No. Dual voltage is a built-in property of the device, so no extra gear is needed. A voltage converter is external equipment that single-voltage devices need on a mismatched grid.
Related guides
Guidance only — not professional electrical advice. Always confirm against your device's label before plugging in. Local wiring (especially in hotels and older buildings) can vary.