**An amperage calculator works by entering at least two variables needed for the calculation, which can include volts (V), resistance (R) and power (P).** In physics, there are many different formulas where I, the current in amps, can be given in terms of these other variables, including I = V/R, I = P/V and I = sq.rt.(P/R).

In these different formulas used in circuitry, P is power given in watts, R is the resistance in ohms and V is the voltage in volts. With the formulas given above, students can calculate amperage if they know two of these variable. For example, to solve for the amperage I in the formula I = V/R requires that the value of the variables V in volts and R in ohms be given.

Similarly, using an online amperage calculator, such as the one provided by RapidTable, requires entering at least two variables. This calculator then gives the other required variables. For example, entering V = 20 and R = 5 and pressing the "Calculate " button gives the result of 4 as the amperage I and 80 as the power in watts. If instead a student is given the power as 80 watts and resistance as 5, then the results are amperage as 4 amps and voltage as 20 volts. To check that the calculator gives the right results, students can input the variable values into any of the formulas for amperage, such as I = sq.rt.(P/R) or I = sq.rt (80/5) = sq.rt.(16) = 4 amps.