Given one of the values for frequency, period, or wavelength (enter a value in feet or meters, not both) returns the other two. The velocity factor is assumed to be 1 if not entered.
Although you don’t normally consider it in most electronics applications, a waveform can have a length. To visualize this, imagine that you have connected a wire to voltage source that is producing a sine wave. Knowing that the signal does not move instantaneously in the wire, envision the signal moving down the wire. As the leading edge of the sine wave moves down the wire, new portions of the sine wave are entering the wire from the voltage source. This is roughly analogous to grabbing the end of a rope and waving it up and down. As you do, the wave you create in the rope moves down its length. The wavelength is the distance, down the wire, for one period of the waveform. The same concepts apply to radio waves.
In a vacuum away from other influences, the signal travels at the speed of light. When the signal is traveling in a cable, this is not the case. In a typical coaxial cable, for instance, the signal travels at about 80% of the speed of light. This is called the velocity factor which is expressed as a number less than 1 (80% = 0.8). For radio work, the velocity factor is typically taken as 1.
The formulas used to convert between the values are shown below.