Ohm's Law defines the relationship between voltage, current, and resistance in an electrical circuit: V = I × R. Combined with the power equation P = V × I, you can solve for any two unknown electrical values when you know the other two. This calculator handles all six possible input combinations instantly.
Enter Any Two Values
Fill in exactly two of the four fields below. The calculator will solve for the other two.
Formulas Used
Ohm's Law Formula Reference
| To Find | Given | Formula |
|---|---|---|
| Voltage (V) | I, R | V = I × R |
| Voltage (V) | P, I | V = P / I |
| Voltage (V) | P, R | V = √(P × R) |
| Current (I) | V, R | I = V / R |
| Current (I) | P, V | I = P / V |
| Current (I) | P, R | I = √(P / R) |
| Resistance (R) | V, I | R = V / I |
| Resistance (R) | P, I | R = P / I² |
| Resistance (R) | V, P | R = V² / P |
| Power (P) | V, I | P = V × I |
| Power (P) | I, R | P = I² × R |
| Power (P) | V, R | P = V² / R |
How to Use the Ohm's Law Calculator
Whether you are designing a circuit, troubleshooting an electrical problem, or studying for an electronics exam, this Ohm's Law calculator gives you instant answers. It combines Ohm's Law (V = IR) with the power equation (P = IV) to solve for any two unknown values when you provide the other two.
Step 1: Enter Two Known Values
Fill in exactly two of the four fields: Voltage (V), Current (I), Resistance (R), or Power (P). For example, if you know a circuit has 12 volts and 2 amps, enter 12 in the Voltage field and 2 in the Current field. Leave the other two fields empty.
Step 2: Click Calculate
Press the Calculate button and the tool instantly computes the remaining two values. In our example, resistance would be 6 ohms (R = V / I = 12 / 2) and power would be 24 watts (P = V × I = 12 × 2). All six possible input combinations are supported.
Step 3: Review Results and Formulas
The results appear in clear stat cards showing all four electrical values. Below the results, the calculator shows exactly which formulas were used, so you can follow the math and learn the relationships between voltage, current, resistance, and power.
Understanding Ohm's Law
Ohm's Law is the cornerstone of electrical engineering. It states that voltage across a conductor is directly proportional to the current flowing through it, with resistance as the proportionality constant. The formula V = I × R can be rearranged to find any of the three values. Combined with the power equation P = V × I, you get a complete toolkit for basic circuit analysis.
Practical Applications
Use this Ohm's Law calculator to size resistors for LED circuits, determine power supply requirements, calculate wire current capacity, or verify that component ratings are sufficient. Electronics hobbyists building Arduino or Raspberry Pi projects find it especially useful for quick component selection. All calculations run locally in your browser, so your data stays private.
Frequently Asked Questions
Is this Ohm's Law calculator completely free?
Yes, this calculator is 100% free with no limits. You can perform as many calculations as you need without creating an account or paying anything.
Is my data safe when using this tool?
Absolutely. All calculations run entirely in your browser using client-side JavaScript. No data is sent to any server, stored, or logged. Your values never leave your device.
What is Ohm's Law?
Ohm's Law states that voltage (V) equals current (I) multiplied by resistance (R), written as V = I x R. It describes the fundamental relationship between voltage, current, and resistance in an electrical circuit and is the foundation of electrical engineering.
How do I calculate power using Ohm's Law?
Power (P) in watts equals voltage (V) times current (I), written as P = V x I. By combining this with Ohm's Law, you can also calculate power as P = I squared x R, or P = V squared / R. This calculator handles all these derivations automatically.
Which two values do I need to enter?
You need any two of the four values: voltage (V), current (I), resistance (R), or power (P). The calculator will solve for the remaining two values using the appropriate formulas from Ohm's Law and the power equation.
What units does this calculator use?
This calculator uses standard SI units: volts (V) for voltage, amps (A) for current, ohms (ohm) for resistance, and watts (W) for power. For very small or large values, the results are displayed in scientific notation or with appropriate precision.
Can I use this for AC circuits?
This calculator is designed for DC circuits and simple resistive AC circuits. For AC circuits with reactive components like capacitors and inductors, you would need to account for impedance rather than simple resistance. The basic relationships still apply to the resistive portion of AC circuits.
Why does the calculator need exactly two values?
With four unknowns (V, I, R, P) and two independent equations (V = IR and P = IV), you need exactly two known values to solve for the remaining two. Entering fewer gives insufficient information, and entering more may create contradictions.