Ohm's Law Calculator

Created by Luis Hoyos
Last updated: Aug 06, 2022

Welcome to the Ohm's law calculator, a tool created to study the voltage-current-resistance relationship. This calculator has a dynamic behavior so that you can use it in various ways, such as:

  • Resistance calculator;
  • Current calculator;
  • Voltage calculator; and
  • Power calculator.

If you need to learn more, keep reading to learn how to use Ohm's law to calculate resistance, current, and voltage.

What is Ohm's law?

Ohm's law is an empirical law that states the electrical current (I) and voltage (V) between two points of a conductor are directly proportional:

I = V/R

where R is the conductor resistance. From this linear relationship, we can note the inverse of resistance (1/R) is the constant of proportionality.

V, I, and R, the parameters of Ohm's law
V, I, and R, the parameters of Ohm's law. Attribution: Waveguide2, Public domain, via Wikimedia Commons

With the previous formula, we can calculate current, but if we want to calculate resistance with Ohm's law, we express it the following way:

R = V/I

And if we want to calculate voltage, we multiply the current by the resistance:

V = IR

Here are other important points about the terms of the equation:

  • R is a material property that indicates how averse the conductor is to the flow of electrons. The SI unit of resistance is the ohm (Ω). Note that the higher this value, the less current will flow.
  • Current measures the amount of charged particles (electrons, usually) that pass over the conductor per unit of time. The SI unit of current is ampere (A). The movement of charged particles is, in essence, electrical energy.
  • Voltage is the last piece of the cube. We need a source of energy to display the electrical energy through the charged particles. We obtain this energy with a voltage source, which helps create an electric potential (electric potential energy per unit charge). The greater the voltage between the two points, the more current will flow. The SI unit of voltage is the volt (V).

As mentioned before, Ohm's law is empirical; therefore, its application can present some exceptions, depending on whether the circuit devices are resistive or not. Resistive devices are those for which Ohm's law is applicable, and they have the characteristic of having only resistors and no capacitances or inductances. Devices that do possess capacitances or inductances or do not behave according to Ohm's law are known as non-ohmic devices.

Ohm's law to calculate power

By definition, power is the rate of doing work (more about this in our work and power calculator). Electrical power indicates how fast the charged particles use their energy to do work, whose work consists of passing through an electric potential (voltage) difference.

In an electrical circuit, power (P) is defined as the product of the voltage difference times the current flowing through it:

P = VI

As mentioned before, not all circuits follow Ohm's law. For those that do behave according to Ohm's law, we can calculate electrical power in any of the following ways:

P = VI = I²R = V²/R

Calculating Ohm's law for anisotropic materials

Isotropic materials are those that possess the same properties in all directions. In the context of electric circuits, isotropy refers to the uniformity of electrical properties. Most commonly used materials are isotropic, but some materials like wood or graphite are considered anisotropic.

For anisotropic materials, instead of calculating Ohm's law with V = IR, we must use another formulation of the equation, which relates equivalent terms:

E = ρ J


  • EElectric field vector, in volts per meter (V/m);
  • ρ — Electrical resistivity of the conductor, in ohm meter (Ω m); and
  • E — Current density vector, in amperes per square meter (A/m²);

In the previous equation, the electric field vector is analogous to the voltage, resistivity to resistance, and the current density vector to the current in amps.

Luis Hoyos
Voltage (V)
Current (I)
Resistance (R)
Power (P)
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