Ohm's Law Calculator

Online calculator for voltage, current, resistance and power

Calculation

Instructions

Enter two of the four values and click "Calculate". The other two values will be calculated automatically.

Result
U Voltage:
I Current:
R Resistance:
P Power:

Good to know

Ohm's Law

Ohm's law is a fundamental principle of electrical engineering. It describes the relationship between voltage, current and resistance: Voltage equals current multiplied by resistance.

Basic formulas
\[U = I \times R\] \[P = U \times I\]
Voltage = Current × Resistance
Power = Voltage × Current
Units
  • U: Voltage in Volts (V)
  • I: Current in Amperes (A)
  • R: Resistance in Ohms (Ω)
  • P: Power in Watts (W)
Note on power

Electrical power is strictly speaking not part of Ohm's law, but was included here because they are closely related.

Ohm's Law and Power

Ohm's law is a fundamental principle of electrical engineering and electronics. It describes the relationship between voltage, current and electrical resistance. The law states that voltage equals current multiplied by resistance.

Variations of Ohm's Law

Calculate voltage:
\[U = R \times I\]
\[U = \sqrt{P \times R}\]
\[U = \frac{P}{I}\]
Calculate current:
\[I = \frac{U}{R}\]
\[I = \frac{P}{U}\]
\[I = \sqrt{\frac{P}{R}}\]
Calculate resistance:
\[R = \frac{U}{I}\]
\[R = \frac{P}{I^2}\]
\[R = \frac{U^2}{P}\]
Calculate power:
\[P = U \times I\]
\[P = I^2 \times R\]
\[P = \frac{U^2}{R}\]

Practical examples

Example 1: Calculate voltage

Given: Current \(I = 2 \text{ A}\), Resistance \(R = 5 \text{ Ω}\)

\[U = I \times R = 2 \text{ A} \times 5 \text{ Ω} = 10 \text{ V}\]

The voltage is therefore 10 V.

Example 2: Calculate power

Given: Resistance \(R = 4 \text{ Ω}\), Current \(I = 3 \text{ A}\)

\[P = I^2 \times R = (3 \text{ A})^2 \times 4 \text{ Ω} = 9 \times 4 = 36 \text{ W}\]

The power is therefore 36 W.

Applications
Electronics:
• Circuit analysis
• Component calculation
• Power dissipation
• Voltage divider
Electrical engineering:
• Wire calculation
• Motor power
• Heating design
• Energy consumption
Measurement technology:
• Multimeter
• Oscilloscope
• Range adaptation
• Calibration
Important notes
  • Ohm's law applies only to ohmic resistors (linear components)
  • For AC, inductive and capacitive reactances must be considered
  • The power formulas apply to DC and ohmic loads in AC
  • At high frequencies, parasitic effects can influence behavior


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