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

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.