Ohm’s Law Calculator | Calculate Voltage, Current, Resistance & Power
Electronics Tools

Ohm’s Law Calculator

This bidirectional tool solves for Voltage (V), Current (I), Resistance (R), and Power (P) by applying the fundamental principles of electronics: Ohm’s Law formula (V = I × R) and the Power Law (P = V × I).

Simply enter any two known values, and the calculator will instantly determine the remaining two. It features a Live Circuit Visual[Image of an electric circuit diagram] to help students, hobbyists, and engineers visualize the relationship between electrical potential, flow, and impedance in real-time.

Circuit Parameters

Input Any 2
V
A
Ω
W

Status

Waiting for input… (Enter 2 values)

Live Circuit Visual

Diagram
Interactive Ohm’s Law Circuit Diagram + – CURRENT (I) — A VOLTAGE (V) — VRESISTANCE (R) — Ω POWER (P) — W
W

Ohm’s Law Formulas Explained

Ohm’s Law describes the relationship between voltage, current, and resistance in an electrical circuit. Combined with Watt’s Law (Power), these 12 formulas are essential for circuit analysis.

Find Voltage (V)

V = I × R
V = P / I
V = √(P × R)

Find Current (I)

I = V / R
I = P / V
I = √(P / R)

Find Resistance (R)

R = V / I
R = V² / P
R = P / I²

Find Power (P)

P = V × I
P = I² × R
P = V² / R

How to Use the Calculator

Determine any unknown circuit value in 3 simple steps.

1

Enter First Value

Input any known electrical parameter. For example, if you know your battery is 12 Volts, enter that in the Voltage field.

2

Enter Second Value

Input a second known parameter. If you are using a 6 Ohm resistor, enter that in the Resistance field.

3

Get Instant Results

The calculator automatically solves for the missing values (Current and Power) and updates the visual circuit diagram.

Real-World Examples

Understanding Ohm’s Law is critical for practical electronics work. Here are common scenarios:

  • LED Resistor Calculation: If you have a 9V battery and a standard red LED (2V forward drop, 20mA current), you need to drop 7V across the resistor. Using V=7 and I=0.02, the calculator gives R = 350Ω.
  • Heater Power: A 120V space heater draws 12.5 Amps. Entering these values calculates a Power usage of 1500 Watts (1.5kW).
  • Battery Life Estimate: Knowing the current draw (I) of your device helps you estimate how long a battery (mAh capacity) will last.