Voltage Converter Wattage Calculator

The watts × 1.25 figure is a PlugVoltage estimate, not a verified converter requirement. Confirm startup demand, permitted loads and duty cycle with both manufacturers. The site does not recommend conversion for mismatched high-power heating appliances.

Device watts

Use the W number from the label when available.

Or volts x amps

AC: V x A = VA. W = VA x PF. The watts × 1.25 figure is a PlugVoltage estimate, not a verified converter requirement. Confirm startup demand, permitted loads and duty cycle with both manufacturers. The site does not recommend conversion for mismatched high-power heating appliances.

This is a heating device, motor, kettle, dryer, iron, or straightener

Device load: 150⁠W
Headroom: × 1.25
Converter sizing result: ~200⁠W

~200⁠W

~200. The watts × 1.25 figure is a PlugVoltage estimate, not a verified converter requirement. Confirm startup demand, permitted loads and duty cycle with both manufacturers. The site does not recommend conversion for mismatched high-power heating appliances.

Methodology

Quick sizing examples

Label or device	Calculation	Converter result	Use this note
65W laptop brick	65W x 1.25	82W estimate	Small electronics only; most modern laptop chargers are already 100-240V.
Label says 120V 2A	120V x 2A = 240VA; 240VA x 1.25	300VA estimate; confirm W and VA limits	Use the AC input numbers on the label, not a USB output rating.
1500W hair dryer or kettle	High-watt heating load	Do not size a travel converter	Use a dual-voltage travel model, a local appliance, or hotel-provided gear.

Sources and limits

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.

OpenStax: Power in an AC Circuit, section 15.4 · checked: 2026-09-04
For sinusoidal AC, average real power is RMS voltage times RMS current times the power factor. Multiplying the RMS voltage and current alone does not necessarily give real watts. Power factor discussion and RMS average-power equation before Example 15.3. An electrical principle, not a measured power factor, startup demand or converter approval for any appliance. Use manufacturer ratings for the actual load.
SKROSS: World to USB series manual, version 1.2 · checked: 2026-09-04
AC current limits and USB output are separate. In the AC20PD examples a single USB-C port reaches about 20W; simultaneous USB-A + USB-C use shares 15W. PDF page 1, English technical ratings and safety instructions. These figures apply to the named series. The manual prohibits stacking adapters and multiplug sockets; other models require their own manual.
Conair: 1875 W Model 303 hair dryer instructions · checked: 2026-08-21
Conair Model 303 specifies 110–125V AC, 60Hz and prohibits use with a voltage converter. PDF page 1, important safety and operating instructions. This label excludes Japan’s 100V. It does not describe every hair dryer.

How much headroom do I need?

AC volts multiplied by amps gives apparent power in VA. Real power in watts also depends on power factor. Neither calculation establishes startup demand or manufacturer approval.

When not to use a converter

Hair dryers, kettles, curling irons, and flat irons can draw 1000–3000W. A travel converter that claims to handle that load is often bulky, hot, or unsafe in real use. A dual-voltage travel model or a local appliance is the safer answer.

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