The field rate of an interlaced video image is twice the effective frame rate, since interlacing draws only half of the image (the odd- or even-numbered lines) at a time. For example, a field rate of 60 Hertz will correspond to a 30 frames-per-second moving picture. A field rate can apply to either a video signal, or to a monitor designed to display that signal without conversion.

Theoretically, an interlaced signal could have three or more fields per frame, resulting in a field rate that is a 3x or higher multiple of the frame rate. However no such signal is in common use today.

Progressive scan monitors do not have a field rate, however they may still display interlaced video by converting each field into a full frame, a process called deinterlacing. In this case, the monitor's frame rate would then likely match the video signal's field rate.