Ohm's Law Calculator
Calculate voltage, current, resistance, or power using Ohm's Law. Enter any two values to find the others. Essential tool for electronics engineers, students, and hobbyists working with electrical circuits. Understand the fundamental relationship between voltage (V), current (I), resistance (R), and power (P) in DC circuits.
Solve For
Click a variable to solve for it
Enter Known Values
Enter at least two values to calculate Power
Enter at least two known values to calculate the result
All Formulas
Ohm's Law
Power Formulas
Quick Examples
Understanding Ohm's Law
Ohm's Law is one of the most fundamental principles in electronics and electrical engineering. Discovered by Georg Simon Ohm in 1827, it describes the relationship between voltage, current, and resistance in an electrical circuit.
The law states that the current flowing through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance. This relationship is expressed as V = I × R.
Voltage (V) is the electrical pressure that pushes electrons through a circuit, measured in Volts.
Current (I) is the flow rate of electrons, measured in Amperes (Amps).
Resistance (R) opposes current flow, measured in Ohms (Ω).
Power (P) is the rate of energy transfer, measured in Watts.
How to Use Ohm's Law Calculator
- Enter any two known values (voltage, current, resistance, or power)
- Click on the variable you want to solve for
- The calculator automatically computes the missing value
- Use the formula reference to understand the relationship
- Verify your results with the quick examples provided
Common Examples
Calculate Current: 12V Battery, 100Ω Resistor
Voltage: 12V, Resistance: 100Ω. Using I = V/R: Current = 12V / 100Ω = 0.12A (120mA).
Calculate Resistance: 5V Supply, 20mA LED
Voltage: 5V, Current: 20mA (0.02A). Using R = V/I: Resistance = 5V / 0.02A = 250Ω.
Calculate Power: 9V Battery, 0.5A Current
Voltage: 9V, Current: 0.5A. Using P = V×I: Power = 9V × 0.5A = 4.5W.
Common Mistakes to Avoid
- Forgetting to convert mA to Amperes (divide by 1000)
- Mixing up kΩ and Ω (multiply kΩ by 1000)
- Using wrong formula for power calculations
- Not accounting for voltage drops in series circuits
- Ignoring power dissipation limits in components
Frequently Asked Questions
What is Ohm's Law?
Ohm's Law states that voltage (V) equals current (I) times resistance (R): V = I × R. It's fundamental to understanding electrical circuits.
Do I need to enter all values?
No, you only need to enter any two values. The calculator will solve for the third (or fourth if calculating power).
Can I calculate power with this tool?
Yes! Enter voltage and current, or resistance and current, and click on power to calculate it using P = V×I or P = I²×R.
What units should I use?
Voltage in Volts (V), Current in Amperes (A), Resistance in Ohms (Ω), Power in Watts (W). Convert mA to A by dividing by 1000.
Does this work for AC circuits?
Ohm's Law applies to DC circuits. For AC circuits, you need to consider impedance, phase, and frequency.