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Ohms Law Calculator

Ohm’s law is an important fundamental law of physics and electricity. It was proposed by the German Physicist Georg Simon Ohm.

Ohm’s law states that:

The current flowing through a circuit with certain resistance is directly proportional to the voltage difference across the two points.

Stating in the form of expression, Ohm’s law says:

R= V/I, where V, I and R are the voltage, current, and resistance of the given circuit respectively.

Ohm’s law is popular in all its three forms: V= IR, I = V/R, and R = V/I

In this expression, we need to observe three main terms of electricity: Voltage, Current, and Resistance of an electrical circuit.

Let us understand these terms better here:

Electrical Circuit

It is the path in which various electrical components such as the source of power and the electrical appliances that are working by utilizing the power are connected through an electrical conductor.

Note that current flows only in closed circuits, which means there should be a closed path for the current to flow.

In an electrical circuit, there can be many types of elements: power consuming, power generating, resistances, inductances and capacitances and many such.

Note that Ohm’s law is valid only for electrical circuits that have pure resistance in them.


For current to flow, there must be a difference in potential or electrical charge. For example, take the analogy of water flow from one area to another. Water flows only where there is a difference in the altitudes or pressures between the areas. Otherwise, water does not flow.

Similarly, for the current to flow between them, there should be a difference in the electric potential or charge between them. This difference in charge is said to be the voltage between those two points. The higher the potential difference or voltage between two points. This is what Ohm’s law says.

  • The unit of voltage is Volts and is denoted by the letter ‘V’.

  • The concept of voltage was first studied and explained by Italian physicist Alessandro Volta, the originator of chemical batteries.

  • Voltage is measured by an instrument called Voltmeter.


Current is the flow of electrical charge. We all know that electrons are responsible for the flow of current. When excited due to any form of external energy such as light, heat, magnetism or electrical charge, electrons of certain substances get energized and break their bonds, become free electrons and their charge flows throughout the circuit in which they are connected to. This flow of charge is what constitutes Electrical Current.

  • The unit of electrical current is ‘ampere’ or ‘amp(s)’ in short. It is denoted by the letter ‘I’ or ‘I’.

  • The discovery of electricity is attributed to many great scientists – Benjamin Franklin, Thales, Gilbert, Alessandro Volta, Thomas Alva Edison, and Nikola Telsa.

  • Current is measured by an instrument called Ammeter.

Every metal has a certain power....of setting the electric fluid in motion. – Alessandro Volta


It is the nature of every electrical conductor to oppose the free flow of current through it. This is called its Resistance. This is different for every conducting material or conductor and is a property of its parameter called Electrical Resistivity, denoted by the Greek letter, ρ.

The resistance, denoted by R, of a conductor is given by R= ρ x l/A, where l is the length of the conductor and A is the area of the cross section of the conductor.

Besides electrical conductivity, the resistance of a material depends on:

  • The area of cross section – more the area of cross section, lesser the resistance.

  • The length of the conductor – higher the length, greater is the resistance.

  • Temperature of the conductor – higher the temperature, more freedom for the electrons to flow, hence less resistance.

Note: Only resistance varies with the above mentioned parameters, but not the resistivity. Resistivity of a substance is fixed by its inherent nature.

Key Points about Resistance

  • A resistance element cannot store energy. It can only dissipate energy and get the work done instantaneously.

  • Examples of resistors that we use in day to day life include laptop charger, a fan speed controller, mobile charger, and sensors in electronic circuits.

  • The unit of resistance is Ohms, denoted by Greek letter Ω, pronounced as Omega.

  • The resistance of an electrical circuit is measured by an instrument called Ohmmeter.

Ohm’s Law and Electrical Power Calculations

Ohm’s law is not just confined to the calculation of current flowing in an electrical circuit. It also helps in calculating the power utilized by a resistive element in an electrical circuit.

The power P consumed by a resistive element is given by the product of voltage drop across its terminals and the current flowing through it. The unit of power is Watts, represented by the symbol W.

P = V x I, W

From Ohm’s law:

We know that V = I x R,

  • P = I x R x I = I2 R, W

Electrical Energy

Power, when multiplied by the time for which it is being utilized, gives the electrical energy consumed. Thus, the electrical energy consumed by an electrical appliance is given by the product of kilowatts (or thousands of watts) multiplied by time in hours.

Next time when you purchase an electrical appliance:

Observe that is marked in kilowatt-hours(kWh). Appliances are rated in kWh because it is easy to work with this unit in day to day life rather than working with thousands and millions of joules.

The common unit of electricity is one kilo-watt hour or 1 kWh. We pay our electricity bill based on how many kilowatt hours our appliances have consumed in a given month. Want to know more about how prices of electricity are fixed and why we end up paying so huge electricity bills some times? Check more facts at our free online Electricity bill calculator.

Some interesting facts about Ohm’s Law

  • Ohm’s law was first observed by Henry Cavendish, who was attributed to the discovery of Hydrogen. However, Cavendish did not publish his studies on Ohm’s law during his lifetime at all. Hence, the law is credited to Georg Simon Ohm, on whose name it became well renowned.

  • Georg Simon Ohm
    Georg Simon Ohm, the Father of Ohm’s Law.
    Image Source: Wikipedia

  • Ohm’s law holds true only for resistance elements. For other types of elements, that have inductance and capacitance, Ohm’s law is not valid. Such electrical materials for which Ohm’s law is not applicable are called non-Ohmic materials.

  • Ohm’s law is applicable only to circuits that run on direct current (DC), not the ones that work with alternating currents (AC). This is because, in AC circuits, inductance and capacitance come into the picture, which do not follow Ohm’s law.

  • What is called as resistance for DC circuits, is termed as Impedance for an AC circuit. Our online free reactance calculator will help you better.
  • An electrical instrument that can measure various electrical parameters, including resistance, voltage, and current of a circuit is called a multimeter.

  • In practice, resistance is both a useful resource and a wastage – we use resistance in many forms for good purposes, however, more resistance means more power needed to get the work done and more heating losses.

How CalculatorHut’s Ohm’s law calculator helps you?

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“It is easier to resist at the beginning than at the end.” ― Leonardo da Vinci

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