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Measure before you size

Replace the guess with a real watt.

A charger label is a ceiling, a compressor cycles and a motor starts differently from how it runs. Choose the measurement path that matches the circuit, then use the result in the calculators.

Choose a measurement path →
Measurement path

What are you measuring?

Do not bridge circuit types with a travel adapter or improvised cable. Start with the electrical path itself.

USB-A and most USB-C power pathsVoltage, current, capacity, energy and calculated resistance
Klein Tools

ET920 USB Digital Meter

Checking phone, tablet and compatible USB-C charging energy without opening a mains circuit.

3–20V DC · up to 3A USB-A / 5A USB-C
Already have a measurement?Use average watts for runtime and observed peak for output.
Open Runtime Lab →
A calmer measurement method

One load. One complete cycle. One honest margin.

  1. 01Use a meter designed for the exact AC, USB or DC path.
  2. 02Measure long enough to include cycling, standby and normal use.
  3. 03Keep average watts, total Wh and the highest observed start separate.
  4. 04Enter the result in Runtime Lab, then leave a reserve for uncertainty.