How large (in watts) of a UK plug converter should I use?

I’m trying to find the right travel “US plug to UK plug” converter to buy, but I’m unsure of how many watts the device uses. The device description says: “AC100V, 50/60Hz, DC5V, 1.2A” online regarding the adapter, but I don’t know how many watts a 5V would be. Can anyone help me?

To convert between currents and wattages:

Power = Current(squared) * Resistance

also, Voltage = Current * Resistance

As your device uses 5 volts, and 1.2 amps, its resistance is 5/1.2 = 4.16 ohms.

so then,
Power = 1.2(squared) * 4.16
Power = 6 watts

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