Ohm's Law Calculator
Enter any two values and click calculate to find the third using Ohm's Law: V = I × R
Calculated Result
Interactive Circuit
Understanding Ohm's Law
Ohm's Law describes the relationship between voltage (V), current (I), and resistance (R) in an electrical circuit:
V = I × R
Voltage = Current × Resistance
I = V ÷ R
Current = Voltage ÷ Resistance
R = V ÷ I
Resistance = Voltage ÷ Current
Voltage (V)
Measured in Volts (V)
Current (I)
Measured in Amperes (A)
Resistance (R)
Measured in Ohms (Ω)
Detailed Guide to Ohm's Law
Real-World Examples
LED Circuit
When powering a 2V LED with a 5V source, you need a resistor to limit current. Using Ohm's Law with a desired current of 20mA: R = (5V - 2V) ÷ 0.02A = 150Ω
Phone Charger
A 5V phone charger delivering 2A to charge your phone is applying Ohm's Law. The phone's internal resistance determines the current flow: R = 5V ÷ 2A = 2.5Ω
Common Mistakes to Avoid
Using incorrect units
Always use volts (V), amperes (A), and ohms (Ω). Convert mA to A by dividing by 1000.
Forgetting voltage drops
In circuits with components like LEDs, remember to subtract their voltage drops from the source voltage.
Tips for Success
Double-Check Units
Always verify you're using the correct units before calculating.
Use Round Numbers
For quick estimates, round to the nearest standard resistor value.
Safety First
Always calculate maximum power ratings for components.
Related: Power Calculation
Power (P) in watts can be calculated using Ohm's Law values:
P = V × I
Power = Voltage × Current
P = I² × R
Power = Current² × Resistance
P = V² ÷ R
Power = Voltage² ÷ Resistance