Power plugs and adapters in the USA

The USA power plug comes in two types, Type A and Type B, and US sockets supply 120 V at 60 Hz. Canada and Japan use the same two plug types. A USA adapter changes the shape of your plug and nothing else. Whether your device can run on 120 V is a separate question, and the label on the device answers it.

The plug letters here belong to Electrical Safety First (ESF), a UK registered charity, because IEC's own list refused our read, as did the TSA, FCC and CPSC sites. We read the figures below on 3 November 2026 on the pages of ESF, the FAA, the US Commerce and Energy departments and the Los Angeles County District Attorney. OSHA's regulations and a PDF from the Electrical Safety Foundation International (ESFI) supply the rest.

Does your country's plug fit a US socket?

Your country's plug fits a US socket only if it is Type A or Type B, the two types ESF lists for the USA. Type A has two flat parallel pins, and Type B adds a round earth pin.

The letters and supply figures in the table are ESF's. The last column is our own reading of ESF's shape descriptions, not a sentence on its pages. A "No" there means you need a USA adapter for the shape, whatever the voltage. Europe has no single type, so a reader from a country not listed should look up that country on ESF's site.

Voltage figures differ between ESF and the US Commerce Department. Commerce prints 240 V for the UK and Australia and 220 V for India. For Japan it gives 100 V with 50 Hz in the east and 60 Hz in the west. For Brazil it says most states use 110 V, some use 220 V, and "there is no standard voltage".

The Department of Energy writes the US supply as a range, 110-120 V at 60 Hz. Treat a country's figure as a guide, and let your device's label decide.

What does the missing earth pin on a Type A plug mean for your device?

The missing earth pin on a Type A plug means no earth connection, and ESF calls Type A "an ungrounded plug". Appliances built to work without an earth are double-insulated. ESF says they carry a mark of "two squares, one inside the other".

ESF also says an adapter with no earth connection "should only be used with double-insulated equipment". Look for those two squares before you use such an adapter.

Will a three-pin Type B plug go into an old two-slot outlet?

A three-pin Type B plug will not go into an old two-slot outlet, because the outlet has no hole for the round pin. OSHA's workplace rules show these outlets remain legal. New receptacles "shall be of the grounding type", but a "nongrounding-type receptacle" may be replaced with another one.

ESF's advice for a plug that will not go in is short: "Don't force it into a socket if it doesn't fit." Find another outlet, one with the round hole.

Does a USA adapter change the voltage or frequency?

A USA adapter does not change the voltage or the frequency. ESF says travel adapters "do not convert the voltage or frequency", and their only job is to let your plug enter a foreign socket. Check the adapter's own maximum power rating too, since ESF says your appliance must not exceed it.

Changing the voltage takes a voltage converter or transformer. ESF says most of them come with plug adapters, so you may not need a separate one.

Frequency can matter even when the voltage is fine. ESF's example is that "a 50Hz clock may run faster on a 60Hz electricity supply".

How do you read the INPUT line on a charger or appliance label?

The INPUT line on a charger or appliance label states the supply it accepts. ESF's example is "INPUT: 110-240V", found on the rating plate on the appliance or its power supply. ESF says that label means the appliance can work with any supply between 110 V and 240 V.

A range that includes 120 V means a USA adapter is all you need. ESF says a device that is "dual voltage rated" needs no voltage converter or transformer.

A label without 120 V in its range is the case to stop at. ESF says it can be "extremely dangerous" to use an appliance rated at a voltage different from the supply. For the network side of a phone, see our guide to phone, data and eSIM in the USA.

What limits a voltage converter, and which appliances does it not suit?

A voltage converter is limited by its maximum power rating, given in amps or watts, and ESF says your appliance must not exceed that rating. ESF adds that some "electronic" appliances, such as game consoles, televisions, radios and computers, "aren't suitable for use with converters". If you are unsure, ESF says to check with the manufacturer first.

None of the pages we could read names a hair dryer or a kettle, or says what one does at the wrong voltage, so we will not guess. Read the appliance's own plate, then compare its rating with the converter's.

How large a power bank may you carry on a flight in the USA?

A power bank on a US flight must go in carry-on baggage, and the size decides whether it needs approval. The regulation, 49 CFR 175.10, says a power bank "must be carried as spare batteries". The limits below are from the FAA's page.

Watt-hours (Wh) are volts multiplied by amp-hours (Ah), the FAA says, and for milliamp-hours you divide by 1,000 first. Our own example: a power bank printed 10,000 mAh at 3.7 V is 10 Ah times 3.7 V, or 37 Wh. Newer lithium-ion batteries have the Wh figure marked on them, the FAA adds.

Battery terminals must be protected from short circuit, and the FAA's examples are retail packaging or tape. If your cabin bag is checked at the gate, take spare batteries and power banks out of it first.

Airlines may be stricter than these rules. The FAA says many, domestic and international, "may have stricter quantity and Wh limits", so check your airline's own page. The FAA's chart adds that TSA security and international rules may be more restrictive too.

What did Los Angeles County warn about public USB chargers?

The Los Angeles County District Attorney's Office warned on 8 November 2019 that travellers should avoid public USB charging stations in airports, hotels and other locations. Its alert said criminals "load malware onto charging stations or cables they leave plugged in". It said the malware may lock the device or export data and passwords.

The alert's advice was to carry your own AC and car chargers. In its words: "Use an AC power outlet, not a USB charging station." The alert gives no count of incidents and we read no later update, so we cannot say how common this is.

What do the TEST and RESET buttons on a GFCI outlet do?

The TEST and RESET buttons on a GFCI outlet (a ground-fault circuit interrupter) cut the power and restore it. ESFI's test uses a nightlight or similar device:

1. Push RESET, plug in the nightlight and check that it is on.
2. Press TEST. The light should turn off.
3. Push RESET again. The light should turn back on.

A light that stays on after TEST means the GFCI is not working properly, and ESFI says malfunctioning GFCIs "do not provide shock protection". ESFI's PDF does not say why an outlet trips on its own.

OSHA's rule requires GFCI protection for bathroom receptacles in workplaces. That rule says nothing about guest rooms, and we did not read the National Electrical Code.