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Ohms Law Calculator
Ohm's law links voltage, current and resistance. Enter any two values and the calculator finds the others, including electrical power.
Ohm's Law Calculator
V = I × R — find voltage, current, resistance, or power
V = I × R | P = V × I = I²R = V²/R
V
A
Ω
Voltage
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Voltage (V)
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Current (I)
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Resistance (R)
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Power (P)
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Step-by-Step
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About the Ohms Law Calculator
Ohm's law links voltage, current and resistance. Enter any two values and the calculator finds the others, including electrical power.
How to use the Ohms Law Calculator
- Fill in any two of Voltage (V), Current (I), Resistance (R) and Power (P).
- Press the matching Find button, or Calculate, to get the missing values.
Formula and method
V = I × R · I = V ÷ R · R = V ÷ I · P = V × I = I² × R = V² ÷ R
Worked example
12 V across a 4 Ω resistor gives I = 12 ÷ 4 = 3 A and P = 12 × 3 = 36 W.
LED resistor. To run an LED at 20 mA from a 5 V supply with a 2 V drop across the LED, the resistor drops 3 V, so R = 3 ÷ 0.02 = 150 Ω.
When to use the Ohms Law Calculator
- Finding the current, voltage or resistance in a simple circuit.
- Choosing the right resistor for an LED.
- Checking electronics homework and lab results.
Common mistakes to avoid
- Using milliamps as if they were amps.
- Applying Ohm's law to components that do not follow it, such as diodes.
Tips
- Voltage is measured in volts, current in amps, resistance in ohms and power in watts.
- Always check that a resistor's power rating is higher than the power it will dissipate.
Frequently asked questions
Does Ohm's law apply to every component?
It applies to ohmic materials such as resistors. Diodes and transistors do not follow a straight-line relationship.
What is Ohm's law?
The voltage across a conductor equals the current through it multiplied by its resistance.
What units are used?
Volts (V), amperes (A) and ohms (Ω).