Ohm's Law Calculator - Calculate Voltage, Current, Resistance

⚡ Calculate with Ohm's Law

Enter any two values and leave the others blank. The calculator will solve for the missing values.

Voltage (V) The electrical potential difference (volts)

Current (A) The flow of electric charge (amperes)

Resistance (Ω) Opposition to current flow (ohms)

📐 Understanding Ohm's Law

V = I × R

Voltage equals Current times Resistance

Ohm's Law is the fundamental relationship between voltage, current, and resistance in electrical circuits. Discovered by Georg Ohm in 1827, it states that the current through a conductor is directly proportional to the voltage across it.

All Formula Variations

Find Voltage

V = I × R

Find Current

I = V ÷ R

Find Resistance

R = V ÷ I

Find Power

P = V × I

What Each Unit Means

Voltage (V) - Measured in Volts. Think of it as electrical "pressure" that pushes electrons through a circuit.
Current (I) - Measured in Amperes (Amps). The rate of electron flow through a conductor.
Resistance (R) - Measured in Ohms (Ω). How much a material opposes current flow.
Power (P) - Measured in Watts (W). The rate at which energy is consumed or produced.

💡 Practical Examples

Example 1: Finding Current

A 12V car battery powers a 24Ω fog light. How much current flows?

I = V ÷ R = 12V ÷ 24Ω = 0.5A (500mA)

Example 2: Finding Voltage

An LED circuit has 20mA flowing through a 150Ω resistor. What's the voltage drop across the resistor?

V = I × R = 0.020A × 150Ω = 3V

Example 3: Finding Resistance

You want to limit current to 10mA from a 5V source. What resistor do you need?

R = V ÷ I = 5V ÷ 0.010A = 500Ω

Example 4: Calculating Power

A 100Ω resistor has 12V across it. How much power does it dissipate?

I = 12V ÷ 100Ω = 0.12A
P = V × I = 12V × 0.12A = 1.44W
(You'd need at least a 2W resistor!)

❓ Frequently Asked Questions

Does Ohm's Law apply to all components?

Ohm's Law applies to ohmic (linear) components like resistors and wires. Non-linear components like diodes, LEDs, and transistors don't follow Ohm's Law because their resistance changes with voltage/current.

What's the difference between AC and DC for Ohm's Law?

For DC circuits, Ohm's Law applies directly. For AC circuits, you need to consider impedance (Z) instead of just resistance, which includes capacitive and inductive reactance: V = I × Z.

Why is power important?

Power tells you how much heat a component generates. If you don't choose a resistor with adequate wattage rating, it will overheat and potentially catch fire. Always select a resistor rated for at least 2x the calculated power dissipation.

How do I convert between mA and A?

1 Ampere (A) = 1000 milliamperes (mA). To convert mA to A, divide by 1000. For example, 20mA = 0.020A.

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