- The ratio of two relative bandwidths for a bandpass or a bandstop filter. For example, the ratio of the 60 dB rejection bandwidth, to the 3 dB bandwidth of the passband.
- For a low-pass or high-pass filter, the ratio of a stopband frequency to a cutoff frequency.
- A function which takes into account the ratio of the diameter to length of a coil when computing its inductance. Also called form factor (2).