Productive ToolboxOhm's Law Calculator
Calculate Voltage, Current, or Resistance instantly using Ohm's Law (V = I × R).
Ohm's Law Calculator
Enter any two values securely to calculate the third automatically.
Fill exactly two fields to calculate the third automatically.
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❓ What is the Ohm's Law Calculator?
The Ohm's Law Calculator is an interactive web-based tool designed to solve simple electrical circuits automatically. Utilizing Ohm's Law, this tool instantly calculates the missing variable—be it Voltage (V), Current (I), or Resistance (R)—when the other two are provided.
We do not collect or store what you enter. This means lighting-fast computations without data privacy concerns or server latency. This makes it an ideal study companion and a practical assistant for electrical engineers, technicians, and hobbyists.
🛠️ How to Use the Calculator
Enter two values
Type any two of voltage, current and resistance, and set each one's unit: mV, V or kV; µA, mA or A; Ω, kΩ or MΩ.
Read the third
The calculator works out the empty field with V = I × R as you type. If all three are filled, clear one.
Copy or save
Copy the result or save it to the history kept.
🧮 The Ohm's Law Formulas
Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across those two points. Our integrated tool uses the three variations of this core mathematical principle depending on which inputs you deliver:
Voltage (V)
Found by multiplying current with resistance.
Current (I)
Found by dividing voltage by resistance.
Resistance (R)
Found by dividing voltage by current.
Frequently Asked Questions
What is Ohm's law?
The voltage across a resistor equals the current through it times its resistance: V = I × R. Rearranged, I = V ÷ R and R = V ÷ I. For example, 12 V across 6 Ω drives 2 A.
How do I calculate current from voltage and resistance?
Divide voltage by resistance: I = V ÷ R. A 9 V battery across a 450 Ω resistor gives 9 ÷ 450 = 0.02 A, or 20 mA.
How do I pick a resistor for an LED?
Subtract the LED's forward voltage from the supply and divide by the current you want: R = (V supply − V LED) ÷ I. A 2 V red LED at 20 mA on 5 V needs (5 − 2) ÷ 0.02 = 150 Ω. Enter 3 V and 20 mA here to get the same answer.
How do I work out power?
Multiply voltage by current: P = V × I, so 12 V at 2 A is 24 W. Equivalent forms are P = I² × R and P = V² ÷ R. This calculator gives V, I and R; use the electrical power calculator for watts.
Does Ohm's law apply to every component?
It holds for resistors and most conductors at a steady temperature. LEDs, diodes and transistors are non-linear, and a filament bulb's resistance rises as it heats up. In AC circuits with capacitors or inductors, use impedance (Z) in place of R.
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