The Ohm, is a unit of electrical resistance. If a source of 1 Volt is applied to a 1 Ohm resistance, a current of 1 Amp will flow through the resistor and 1 Watt of power will be dissipated. This relationship is known as Ohms Law.

A diagram of this is shown below right. It consists of a Voltage Source, E, connected to a Resistance, R, and indicates the Current, I, that flows through the circuit. Although not readily apparent, Power, P, is still a prime factor and is generally dissipated by the resistor.

The Ohm's Law Wheel below is intended to show the relationship of the Ohm's Law equations. To use the wheel manually, start at the center circle and select the value you need to find; for example, I (Amps), R (Ohms), E (Volts) or P (Watts). Then select the formula containing the values you know from the outer chart circle.

Or you can use the calculator below. It shows that if you have any two parameters, you can calculate the other two. The Wheel will change according to your selection, highlighting the formulas used to obtain the two unknown values.

Note: If you select the same input data type in both selectors, no meaningful calculations can be performed.

The equations behind the entry box above assume that Voltage is in Volts, Current is in Amperes, Resistance is in Ohms, and Power is in Watts. If any of the quantities are expressed in other units they must be converted to the base units. For example, 10 milliamps would need to be converted to the equivalent 0.010 amps.