Ohm's Law - Calculate Resistance

Calculator for electrical resistance, voltage and amperage, with different units. Ohm's law states that resistance is voltage divided by amperage. The formula is R=U/I, the unit is ohm, its symbol is the omega, Ω=V/A. Electrical resistance is a measure of the impediment to the flow of current in an electrical conductor. The lower the resistance, the better the current conducts.

Please select the units and enter two values. The third value will be calculated.

Example: if there is a voltage of 240 volts and a current flow of 3 amperes, then the resistance is 80 ohms.

Ohm's law is probably the best-known physical formula in connection with electricity and it is conveniently simple and understandable. It states that electrical resistance is calculated from voltage divided by current. If there is a high voltage but only a low current, then the resistance of the circuit is high. Good conductors have as low a resistance as possible, the best conductive metal under normal conditions is silver, but for cost reasons copper or aluminium are usually used. The thickness of the material is also important, thick cables conduct better, thin ones have a higher resistance. Electrical energy is often converted into thermal energy in resistors, the resistor gets hot and can melt in extreme cases. Ohm's law was discovered in 1825 by Georg Simon Ohm through extensive experimentation with the very limited possibilities of his time.
You rarely come across the outdated unit mho, or ohm written backwards, which is the reciprocal fraction of ohm. This unit for electrical conductance is now called siemens, the more siemens, the fewer ohms, the better the conductivity, the lower the resistance. The 80 ohms from the example above correspond to 0.0125 siemens or mho.

Physics commonly uses SI units. Here is a calculator to convert units.