How this calculator works
Insertion loss measures how much power delivered to a load changes when a device is added. A power ratio uses ten times its base-ten logarithm; an equal-impedance voltage ratio uses twenty because power is proportional to voltage squared. Positive loss means attenuation, zero means unchanged delivery and negative loss means net gain. This comparison is not return loss, which describes reflection.
Formula
IL = 10 log10(Pbefore/Pafter) = 20 log10(Vbefore/Vafter) for equal real impedances. Pafter = Pbefore 10^(-IL/10).
Worked example
A drop from 100 W to 10 W is 10 dB insertion loss. A voltage change from 10 V RMS to 1 V RMS at the same load impedance is 20 dB loss.
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Frequently asked questions
Can loss be negative?
Yes. It indicates that inserting the device increased the delivered power, as with an amplifier.
Can I compare voltage across different loads?
The simple 20 log voltage relation assumes equal real impedances. Use actual delivered powers when impedances differ.
Why is zero output rejected?
An exactly zero output has infinite loss. The finite decibel calculator requires positive measurements.