A megaohm is equivalent to 1,000,000 ohms. In physics, an ohm is the measure of electrical resistance of a circuit. Ohms are related to voltage V and the electric current I with the equation known as Ohm's law.
Ohm's law states that the electrical current is equal to the ratio of the voltage to the resistance, or I = V/R. The units used for these variable are that I is given in amperes, R is in ohms and the voltage is in volts. Using this equation, one can see that it can be expressed in terms of resistance as R = V/I. George Ohm formulated this law, and the unit of resistance is named in his honor.