Ohm's law, expressed as the formula written as V = IR, is the most commonly used mathematical formula in electrical work. The electrical power formula, written as P = VI, is another frequently used electrical math formula.
In electrical math, V = voltage, R = resistance in ohms, I = current in amperes and P = power in watts. Thus, the formula V = RI means "voltage equals resistance times current." This formula can be used to find voltage, resistance or current if the other two variables are known.
Similarly, the power formula, P = VI, can be used to calculate power, voltage or current if the other two variables are known. The power formula is sometimes written as W = VA, where W = wattage and A = amperage. This formula is remembered with the mnemonic device "West Virginia."