Which two values do I need to enter?

Any two of V (voltage), I (current), R (resistance), or P (power). The calculator derives the remaining two.

Which units can I use?

Voltage: V, mV, kV. Current: A, mA. Resistance: Ω, kΩ, MΩ. Power: W, mW, kW. The tool converts everything to base SI internally.

Are the calculations private?

Yes. Everything runs locally in your browser—no data is uploaded or stored.

Which formulas are used?

Ohm’s law: V = I × R. Power: P = V × I = I² × R = V² ÷ R.

Ohm’s Law Calculator – Voltage, Current, Resistance & Power

Ohm’s Law Calculator – Solve V, I, R, and P

Enter any two values. Choose units if needed. Click Calculate to find the other two.

Voltage (V)

Symbol: V

Current (I)

Symbol: I

Resistance (R)

Symbol: R

Power (P)

Symbol: P

Results will appear here.

Formulas Used

Ohm’s law and power relationships:

$ V = I \times R $
$ P = V \times I $
$ P = I^2 \times R $
$ P = \dfrac{V^2}{R} $

Tip: Provide any two quantities (e.g., V and R). The calculator finds the other two and shows the steps.

Frequently Asked Questions

Which two values should I enter?

Any two of: voltage (V), current (I), resistance (R), or power (P).

What units are supported?

Voltage: V, mV, kV. Current: A, mA. Resistance: Ω, mΩ, kΩ, MΩ. Power: W, mW, kW.

Why is my result shown in a different unit?

To keep numbers readable, the tool auto-scales results (e.g., 0.002 A → 2 mA, 1500 Ω → 1.5 kΩ).

Is my data private?

Yes—everything runs in your browser; nothing is uploaded.

Understanding Ohm’s Law

Ohm’s Law is one of the most important rules in electricity. It describes how voltage (V), current (I), and resistance (R) are related:

$$ V = I \times R $$

What the Symbols Mean

V (Voltage): The “push” that moves charges through a circuit, measured in volts (V).
I (Current): The flow of electric charge, measured in amperes (A).
R (Resistance): How much a component resists the flow of current, measured in ohms (Ω).
P (Power): The rate of using or producing energy, measured in watts (W).

The Ohm’s Law Triangle

A common study tip is the Ohm’s Law Triangle. Cover the value you want to find:

$ V = I \times R $
$ I = \dfrac{V}{R} $
$ R = \dfrac{V}{I} $

By remembering just the triangle, you can quickly rearrange the formula to solve for any missing value.

Adding Power to the Mix

Power ($P$) links to voltage and current:

$$ P = V \times I $$

With Ohm’s Law, we can also write:

$ P = I^2 \times R $
$ P = \dfrac{V^2}{R} $

These forms are useful for electronics design—like checking if a resistor can safely handle the power without overheating.

Real-Life Example

Suppose a 9 V battery is connected across a 1.5 kΩ resistor:

Current: $ I = \dfrac{V}{R} = \dfrac{9}{1500} = 0.006 \,\text{A} = 6 \,\text{mA} $
Power: $ P = V \times I = 9 \times 0.006 = 0.054 \,\text{W} = 54 \,\text{mW} $

So the resistor uses about 54 milliwatts of power—a very small amount, which is why this is a safe beginner circuit.

Why Ohm’s Law Matters

Engineers, electricians, and students use Ohm’s Law to:

Design safe circuits.
Calculate resistor values needed for LEDs or sensors.
Estimate battery life in portable devices.
Troubleshoot circuits when something isn’t working.

👉 Tip: Always keep track of units (V, A, Ω, W). Converting to base units first helps avoid mistakes.