What kHz and watts mean on an ultrasonic cleaner

kHz: the frequency

Low frequencies, 25–40 kHz, make large, energy-rich bubbles. They suit sturdy surfaces and heavy dirt such as oil, polishing paste or rust. High frequencies, 80–130 kHz, clean more gently and suit sensitive materials and fine structures, according to the maker Elma.

Of the 143 cleaners in our database with a stated frequency, 139 stay below 80 kHz. The most common figure is 40 kHz (51 models).

Watts: several different figures

A cleaner can carry up to four watt figures, and shops do not always say which one they quote.

• Ultrasonic power: what drives the sound.
• Peak power: a second ultrasonic figure that some makers give. In all 12 cleaners where we have both, it is higher than the ultrasonic power, for example 30 W and 240 W.
• Heater power: what warms the liquid. It says nothing about the cleaning.
• Total power: in the 6 cleaners where we have all three figures, it is the ultrasonic power and the heater power added together.

So compare like with like. A total figure that includes the heater always looks bigger than an ultrasonic figure on its own.

The figures come from the maker or the seller and are not independently tested. We have found no neutral source that says how many watts a given job needs, so we do not rank cleaners by watts.

What tells you more

Whether the cleaner actually cleans. A piece of foil shows it in ten minutes.

The foil test, step by step →