Ohm's Law Calculator: Voltage, Current & Resistance
Calculate voltage, current, or resistance using Ohm’s Law.
What is Ohm’s Law?
Ohm’s Law defines the fundamental relationship between voltage, current, and resistance in an electrical circuit. It states that the current flowing through a conductor is directly proportional to the voltage applied across it, provided the temperature and physical conditions remain constant.
This law is a core principle of electrical engineering and physics and is used to analyze and design electrical and electronic circuits.
Understanding Voltage, Current, and Resistance
Voltage (V) is the electrical potential difference that drives electric charge through a circuit.
Current (I) is the rate of flow of electric charge through a conductor.
Resistance (R) is the opposition a material offers to the flow of electric current.
Ohm’s Law mathematically links these three quantities.
Ohm’s Law Formulas
- 1Voltage (V) = Current (I) × Resistance (R)
- 2Current (I) = Voltage (V) ÷ Resistance (R)
- 3Resistance (R) = Voltage (V) ÷ Current (I)
How to Use Ohm’s Law Step by Step
- 1Identify which quantity you need to calculate.
- 2Measure or enter the known values.
- 3Select the appropriate Ohm’s Law formula.
- 4Substitute the values into the formula.
- 5Solve to get the result with correct units.
Ohm’s Law Examples
Example 1: Calculating Voltage
If a circuit has a current of 2 A and a resistance of 10 Ω, then V = I × R = 2 × 10 = 20 V.
Example 2: Calculating Current
If a voltage of 12 V is applied across a resistance of 6 Ω, then I = V ÷ R = 12 ÷ 6 = 2 A.
Example 3: Calculating Resistance
If a device draws 3 A from a 9 V supply, then R = V ÷ I = 9 ÷ 3 = 3 Ω.
Where Ohm’s Law Applies
Ohm’s Law applies accurately to direct current (DC) circuits and to alternating current (AC) circuits that contain only resistive components.
In AC circuits with capacitors or inductors, resistance is replaced by impedance, and Ohm’s Law must be modified accordingly.
Common Mistakes When Using Ohm’s Law
- Mixing units such as milliamps and amps.
- Applying Ohm’s Law directly to reactive AC circuits.
- Ignoring temperature effects on resistance.
- Using resistance instead of impedance in AC analysis.
Ohm’s Law FAQs
What is the SI unit of voltage, current, and resistance?
Voltage is measured in volts (V), current in amperes (A), and resistance in ohms (Ω).
Does Ohm’s Law apply to all materials?
No. It applies to ohmic materials where current is proportional to voltage. Non-ohmic materials do not strictly follow Ohm’s Law.
Can Ohm’s Law be used for AC circuits?
It applies only to purely resistive AC circuits. For circuits with inductance or capacitance, impedance must be used.
Why is Ohm’s Law important?
It allows engineers and students to analyze circuits, design components, and troubleshoot electrical systems.
Why Use This Ohm’s Law Calculator?
This Ohm’s Law calculator provides a fast and accurate way to compute voltage, current, or resistance using correct physical definitions. It is ideal for students, electricians, hobbyists, and engineers.
Enter known values to instantly solve circuit problems without calculation errors.