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How we measure

This is the method behind the numbers on thisMETER and its sister sites: what each reading means, how to take it so someone else could repeat it, and how much to trust it. Unless a guide says it reports our own readings, its figures come from manufacturer documentation.

Readings we publish

A reading only counts if someone else could repeat it. Any measurement published on this site states the instrument (make, model and its stated accuracy), the setup (what was connected to what, including cables and adapters), the conditions that affect the result, and the date. A number without that context isn’t published.

Power: USB-C, AC and DC

  • On DC, USB-C included, watts are volts multiplied by amps. On AC, volts times amps gives volt-amperes (VA); a plug-in meter’s watt reading also accounts for the power factor, so it can be lower than VA.
  • A meter’s maximum measurable wattage is a limit of the meter, not what a charger delivers; a MAX reading on its display is the highest value it recorded.
  • A USB-C power meter sits in line between charger and device, so the extra cable and the meter itself become part of the circuit. Short, correctly rated cables keep the reading honest.
  • A plug-in watt meter measures what the outlet supplies, including the losses of any charger, adapter or inverter in between.
  • Energy (Wh or kWh) is power over time. Log long enough to capture a full cycle, such as a fridge compressor turning on and off, or a charge from empty to full.

Accuracy, resolution and counts

  • Accuracy is specified as ± (a percentage of the reading + a number of digits). A meter rated ±(0.5% + 2) that shows 100.0 V can be off by up to 0.7 V: 0.5 V from the percentage, plus 2 digits of 0.1 V.
  • Counts set the resolution. A 6,000-count meter shows at most 5,999 counts: up to 5.999 V on its 6 V range, then up to 59.99 V once it switches to the 60 V range.
  • True RMS meters measure non-sinusoidal AC (from inverters, dimmers and variable-speed drives) within their stated crest-factor and bandwidth limits; average-responding meters can be well off on those waveforms.

Safety ratings

Measurement categories (CAT II, CAT III, CAT IV), each paired with a voltage, tell you where on an electrical system a meter can be used: at the same rated voltage, a higher category is built for more severe transients. Use a meter rated for the circuit you are measuring and follow its manual. Mains voltage is dangerous: if you are not trained for it, leave live measurements to a qualified electrician.

Sound

A sound-level figure depends on frequency weighting (dBA approximates human hearing), the time metric (Fast, Slow, or Leq averaged over a stated period), the distance from the source and the room, so two figures only compare when they were taken the same way. Sound level meters are graded Class 1 or Class 2 under IEC 61672; Class 1 holds tighter tolerances.

Cables and signals

A basic cable tester checks wiring: which pins connect to which. Whether a cable can carry a given speed takes a qualification or certification tester. For USB-C, a tester that reads the e-marker chip shows what the cable says it is rated for, not a measured speed.

What we don’t claim

Unless a guide explicitly reports our own readings with the details above, we have not measured the products it covers, and manufacturer figures are labelled as such.