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Ohm's Law Calculator – Voltage, Current, Resistance

Calculate voltage, current, and resistance using Ohm's law

Calculate Ohm's Law

Enter any two values to calculate the third:

Method and source check

Last checked:

Source and implementation check; this is not professional review or advice.

Method

Provide exactly two of voltage, current, and resistance. The calculator rearranges Ohm's law to find the third value, then calculates electrical power.

V = I × R

I = V / R

R = V / I

P = V × I

Variables and units

V
voltage in volts
I
current in amperes
R / P
resistance in ohms / power in watts

Worked example

With 12 V and 6 Ω, current is 12 / 6 = 2 A and power is 12 × 2 = 24 W.

Limitations

  • This models an ideal resistive DC circuit. It does not account for AC impedance, component tolerances, temperature effects, or electrical safety requirements.

Sources

Table of Contents

How to Use

  1. Enter any two values: voltage (V), current (I), or resistance (R)
  2. Leave the value you want to calculate empty
  3. Click calculate to see all calculated values including power
  4. The calculator uses Ohm's law: V = I × R

What is Ohm's Law?

Ohm's law states that the voltage across a conductor is directly proportional to the current flowing through it, provided the temperature and other physical conditions remain constant. It's one of the fundamental principles of electrical engineering.

Named after German physicist Georg Simon Ohm, who discovered it in 1827, Ohm's law is expressed by the equation: V = I × R, where V is voltage, I is current, and R is resistance.

Ohm's Law Formulas

The basic equation can be rearranged to solve for any variable:

  • Voltage: V = I × R
  • Current: I = V / R
  • Resistance: R = V / I

Power can also be calculated using:

  • P = V × I
  • P = I² × R
  • P = V² / R

Units

Standard electrical units:

  • Voltage (V): measured in Volts
  • Current (I): measured in Amperes (Amps)
  • Resistance (R): measured in Ohms (Ω)
  • Power (P): measured in Watts

Applications

Ohm's law is fundamental in:

  • Circuit design and analysis
  • Electronic component selection
  • Power supply design
  • Troubleshooting electrical circuits
  • Electrical safety calculations
  • Battery and power management
  • LED and resistor calculations

Frequently Asked Questions

What is the relationship between voltage, current, and resistance?
According to Ohm's law, voltage equals current multiplied by resistance (V = I × R). If you increase voltage while resistance stays constant, current increases. If you increase resistance while voltage stays constant, current decreases.
Does Ohm's law apply to all materials?
Ohm's law applies to linear, ohmic materials where resistance is constant. Some materials like semiconductors, diodes, and certain conductors have non-linear behavior and don't strictly follow Ohm's law.
How do I calculate power from voltage and current?
Power is calculated by multiplying voltage and current: P = V × I. You can also use P = I² × R or P = V² / R when you know resistance.
What happens if I enter all three values?
This calculator requires exactly two values. Enter any two of voltage, current, or resistance, and leave the third empty. The calculator will verify that the values satisfy Ohm's law.

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