PlugVoltage

Voltage Converter Wattage Calculator

Start with the AC INPUT rating on your device label. Estimate a converter rating, then check the limits before you choose one.

What does the label show?

Use the W number from the label when available.

Converter sizing result

~200⁠W

Device load
150⁠W
Headroom
× 1.25

Estimate rounded up in steps of 25 W or VA.

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

  • 65W laptop brick

    65W x 1.25 ~100⁠W
    Use this note

    Small electronics only; most modern laptop chargers are already 100-240V.

  • Label says 120V 2A

    120V x 2A = 240VA; 240VA x 1.25 ~300⁠VA
    Use this note

    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 this note

    Use a dual-voltage travel model, a local appliance, or hotel-provided gear.

How much headroom do I need?

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.

Use AC INPUT values, not USB output. V × A gives VA; real watts also depend on power factor.

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.

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.

  1. 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.

  2. 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.

  3. Conair: 1875 W Model 303 hair dryer instructions · checked: 2026-09-30

    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.