Given one of the values for RMS voltage, peak voltage or peak to peak voltage, the solver returns the other two. If over specified, the RMS voltage is used.
This solver assumes the values entered are for a sine wave typical of a AC line voltages and voltages derived from them (e.g. the secondary of a transformer). The following figure depicts what is meant by the terms peak (abbreviated as p) and peak to peak (abbreviated as pp).
Unless otherwise indicated, all AC voltages are assumed to be RMS. When a transformer is specified to have a 12V secondary, this is referring to its RMS value. The RMS value of a an AC voltage is the value that will do the same amount of work as the equivalent DC voltage. For instance, a DC voltage of 1V across a 1Ω resistor will cause the resistor to dissipate 1W of power. The same is true of an AC voltage that is 1V RMS. Graphically, the meaning of an RMS voltage is shown in the following figure. In this figure, the sine wave appears full wave rectified. This makes sense given that the RMS value is specified as doing the equivalent amount of work and the polarity of the voltage is therefore irrelevant.
The formula used to convert between the RMS and peak value is:
Although the RMS voltage is convenient value to use when dealing with power, the peak value comes into play in a number of circuit configurations. Suppose you were designing a simple unregulated power supply composed of a transformer, bridge rectifier and filter capacitor. If you choose a 12V transformer, the output of the power supply will be near 16V (the peak voltage - 2 diode drops) rather than 12V because the filter capacitor will charge to the peak value of the waveform.