How to Use Our Ohm's Law Calculator

3 min read

How to Use Our Ohm's Law Calculator

Ohm's Law is the foundation of electrical engineering. Our Ohm's Law Calculator lets you find any electrical value when you know two of the others.

The Core Relationship

V = I x R

Where V is voltage (volts), I is current (amps), and R is resistance (ohms).

Enter any two values and the calculator solves for the third. It also calculates power (P) in watts using P = V x I.

The Four Calculations

• Find Voltage: Enter current and resistance. V = I x R
• Find Current: Enter voltage and resistance. I = V / R
• Find Resistance: Enter voltage and current. R = V / I
• Find Power: Calculated automatically. P = V x I = I squared x R = V squared / R

Practical Examples

LED Circuit: You have a 9V battery and an LED that needs 20mA (0.02A). What resistor do you need? R = V / I = 9 / 0.02 = 450 ohms (use the nearest standard value: 470 ohms)

Home Circuit: A 120V outlet with a 15A circuit breaker can handle: P = V x I = 120 x 15 = 1,800 watts maximum

Wire Sizing: Higher current requires thicker wire to handle the resistance without overheating. Use Ohm's Law to calculate voltage drop across wire lengths.

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