Ohms Law Calculator


Ohm's Law Calculator

Enter ANY three values to calculate the fourth.

✔ Calculate Voltage (V)
✔ Calculate Current (I)
✔ Calculate Resistance (R)
✔ Calculate Power (P)

Download Ohms Law Calculator for iPhone, iPad or Android


  • ‎Ohms Law Screenshot
  • ‎Ohms Law Screenshot
  • ‎Ohms Law Screenshot
  • ‎Ohms Law Screenshot


Ohm’s Law Calculator to calculate and convert the units of Voltage, Resistance, Power and Current. Convert and calculate to or from any of the following, Volts, Amps, Ohm’s or Watts.

V = Voltage (measured in Volts). I = Current (measured in Amps). R = Resistance (measured in Ohm’s). P = Power (measured in Watts)

Calculate Voltage

To Calculate Voltage:

  • Enter a current value
  • Enter a resistance value
  • Enter a power value
  • Tap Calculate

Calculate Resistance

To Calculate Resistance:

  • Enter a power value
  • Enter a voltage value
  • Enter a current value
  • Tap Calculate

Calculate Current

To Calculate Current:

  • Enter a voltage value
  • Enter a resistance value
  • Enter a power value
  • Tap Calculate

Calculate Power

To Calculate Power:

  • Enter a resistance Value
  • Enter a current Value
  • Enter a voltage Value
  • Tap Calculate

Enter ANY three values to calculate the fourth.

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What is voltage?

Voltage is the pressure or electromotive force from an electrical source and is the difference of electric potential between two points measured in Volts (V).

The calculation for voltage is directly linked to the resistance and current of an electrical or electronic circuit.

In the Ohms Law formula voltage is represented by the symbol “V”.

What is resistance?

Resistance is the measure of resistance of a conductor which restricts the flow of electrons, resistance also effects voltage drop.

Resistance is measured in Ohms (Ω), the lower the Ohms value = the lower the level of resistance.

In the Ohms Law formula resistance is represented by the symbol “R”.

Different types of materials offer a different level of resistance. For electrical or electronic circuits a low resistance is required to reduce the effects caused by circuit resistance.

The higher the resistance value the higher the voltage drop will be.

When using the same type of materials (conductors) longer circuits have a higher resistance than shorter circuits.

For calculating voltage drop caused by circuit resistance take a look at our » Electrical Tools and Reference App which includes a Volt Drop Calculator.

What is current?

Electric current is the amount of flow of electric charge between two points, current is measured in Amperes (A) or Amps for short.

In the Ohm’s Law formula current is represented by the symbol “I”.

There are two types of current, AC and DC.

  • AC = Alternating Current
  • DC = Direct Current

AC current is generally the standard used for electrical installations such as your home, office or workshop.

DC is generally used for batteries, other specialist DC equipment and DC power supplies.

What is power?

Electric power is the rate, per unit time, at which electrical energy is transferred by an electric or electronic circuit.

The electrical unit of power is measured in Watts or kW (kiloWatts), 1000w = 1kW.

Types of power:

  • Active Power (P)
  • Reactive Power (Q)
  • Apparent Power (S)

Active power (True Power) is the actual power consumed by a circuit measured in Watts or kW.

Reactive power is the unused power in a circuit measured in Volt-Amps-Reactive (VAR or kVAR).

Apparent power is the combination of Active Power and Reactive Power measured in Volt-Amps (VA or kVA).

Power Factor value has an effect of the above and can be calculated, to calculate Power Factor take a look at our kVA Calculator.

k = kilo (1000).

What is Ohm's Law?

Ohm’s Law was discovered by Georg Ohm, he discovered that an electric current flow is proportional to voltage and inversely proportional to resistance, this formula was named Ohm’s Law after Georg Ohm.

The Ohms Law formula is used for calculating voltage, current and resistance.

Ohm’s Law Calculations:

  • Calculate voltage = current x resistance or V = I x R.
  • Calculate current = voltage ÷ resistance or I = V ÷ R
  • Calculate resistance = voltage ÷ current or R = V ÷ I

Current is measured in Amps, Voltage is measured in Volts and Resistance is measured in Ohms Ω .

Ohm’s Law Triangle: V over IR.

Ohm's Law Triangle

Ohm’s Law Triangle

What is VIR?

VIR are the symbols used in the Ohms Law formula. An easy way to remember the Ohms Law calculation formula is V over I x R.

V I R represent the various electrical units:

  • V = Voltage measured in Volts.
  • I = Current measured in Amps.
  • R = Resistance measured in Ohms.

Get the app

An easy to use Ohm's Law Calculator.

✔ Calculate Resistance
✔ Calculate Current
✔ Calculate Voltage
✔ Calculate Power

Download Ohm's Law for Android and iOS