# Q-factor Inductor

The Q factor of an inductor is given by:

Q=(2*pifL)/R

Is this only the frequency dependent Rf? Or does it also include the series DC resistance?

• The skin effect and proximity effect are embedded into the measurement of Rf that I conducted with a series resonance circuit. So I don't really understand your comment – Weaverworm Jan 26 '16 at 13:06
• It includes that what is in the formula. The ratio of the inductors (imaginary part of the) impedance Z(s) over the real part of Z(s). Usually the real part of Z(s) is equal to the DC resistance but it does not have to be. – Bimpelrekkie Jan 26 '16 at 14:38
• It includes all real resistance, DCR plus AC resistances that are lossy but may be frequency dependent. So Q isn't necessarily a constant. – John D Jan 26 '16 at 15:33
• @John D, Well technically yes, the Q is constant. I mentioned the frequency dependent resistance that is for sure included (I know) so with that given fact the quality factor is constant at a given frequency. Anyhow thanks for the answer. – Weaverworm Jan 27 '16 at 15:21
• My point was that Q isn't constant with frequency, as hysteresis, eddy current, skin effect and proximity losses vary with frequency. Near DC the Q is different from what it would be at 100 MHz. – John D Jan 27 '16 at 16:33

In your formula, $$\2{\pi}fL\$$ repesents the "ideal" purely inductive resistance of the inductor at freuency $$\f\$$. Thus, by dividing this by the $$\R_f\$$ measured resistance at frequency $$\f\$$, you are taking all parasitic resistances into effect (skin effect, DCR, core hysteresis, etc.)