Ohm's Law Calculator
Calculate voltage, current, resistance, or power using Ohm's Law. Enter any two values to find the other two instantly.
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How to use this calculator
V = voltage (volts), I = current (amperes), R = resistance (ohms), P = power (watts). Enter any two values; the other two are derived.
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Enter any two of voltage (V), current (A), or resistance (Ω). Leave the unknown value as 0.
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The calculator solves for the missing value and also computes power.
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Use any consistent SI units — no conversion needed.
Frequently asked questions
What is Ohm's Law?
Ohm's Law states that the voltage across a conductor is directly proportional to the current flowing through it, with resistance as the constant of proportionality: V = I × R. It applies to most metallic conductors at constant temperature.
What is the difference between AC and DC for this formula?
Ohm's Law applies directly to DC circuits. For AC circuits, you use impedance (Z) instead of resistance (R), and the formula becomes V = I × Z. Impedance includes reactance from capacitors and inductors.
How is power calculated from voltage and resistance?
P = V² / R. Alternatively, P = I² × R. These are derived by substituting V = IR into P = VI.
Ohm's Law Calculator — Voltage, Current, Resistance & Power
How to use the ohm's law
This ohm's law gives you instant, accurate results — no registration or download required. Enter your values above and get your result in seconds. The tool is free, works on all devices, and keeps your data private — nothing is stored or shared.
How the ohm's law works
The uses standard formulas used in mathematics, science, and engineering. Enter your inputs, and the tool calculates the result instantly in your browser. No server-side processing means your data stays on your device. Results update in real time as you change inputs.
The four Ohm's Law equations
From the base formula V = IR you can derive three others: I = V/R (current); R = V/I (resistance); P = VI = I²R = V²/R (power). Together these four equations let you solve any combination of known and unknown electrical quantities.
Practical applications
Ohm's Law is used to select the correct resistor value in LED circuits, calculate fuse ratings, design voltage dividers, and troubleshoot short circuits. When a measured current is much higher than expected, resistance has dropped — a common sign of a faulty component or short circuit.
Ohm's law: how it works
Built on well-established mathematical principles, this tool delivers accurate results for students, researchers, and professionals. Enter your values and get instant clarity without specialist software or manual arithmetic.
Who uses this tool?
Teachers, students, engineers, and data analysts use it to verify calculations, check homework, and solve problems faster. It is intuitive enough for beginners while comprehensive enough for professional use.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →