Ohm's Law Calculator
Calculate voltage, current, resistance, and power using Ohm's law
Volts (V)
Amperes (A)
Ohms (Ω)
Watts (W)
Tip: Enter any 2 values to calculate the remaining values. The calculator will automatically determine which values to calculate based on your input.
How to Use This Calculator
Enter Known Values
Enter at least 2 of the 4 values: voltage (V), current (I), resistance (R), or power (P). Leave the values you want to calculate empty.
Calculate
Click the calculate button. The calculator will automatically determine which values to calculate based on your input.
View Results
The calculated values will be displayed. All related values (including power) will be calculated and shown.
Formula
V = I × R
I = V / R
R = V / I
P = V × I = I² × R = V² / R
Where:
- V = Voltage (Volts)
- I = Current (Amperes)
- R = Resistance (Ohms)
- P = Power (Watts)
Example 1:
Voltage = 12 V, Current = 2 A
Resistance = 12 / 2 = 6 Ω
Power = 12 × 2 = 24 W
Example 2:
Resistance = 100 Ω, Current = 0.1 A
Voltage = 100 × 0.1 = 10 V
Power = 10 × 0.1 = 1 W
About Ohm's Law Calculator
The Ohm's Law Calculator is a comprehensive tool for calculating voltage, current, resistance, and power in electrical circuits. Ohm's law is one of the fundamental principles of electrical engineering, stating that voltage equals current times resistance (V = I × R). This calculator allows you to enter any two values and automatically calculates the remaining values.
When to Use This Calculator
- Circuit Analysis: Analyze DC circuits and calculate unknown values
- Component Selection: Determine resistor values for desired current or voltage
- Power Calculations: Calculate power dissipation in circuits
- Educational Purposes: Learn and practice Ohm's law calculations
- Design Verification: Verify circuit designs and component ratings
Why Use Our Calculator?
- ✅ Comprehensive: Calculates voltage, current, resistance, and power
- ✅ Flexible: Enter any 2 values to calculate the rest
- ✅ Automatic: Determines which values to calculate automatically
- ✅ Easy to Use: Simple, intuitive interface
- ✅ Free Tool: No registration or payment required
- ✅ Educational: Includes all formulas and examples
Common Applications
LED Circuits: Calculate the resistor needed to limit current through an LED. For example, with 5V supply and 2V LED at 20mA: R = (5-2) / 0.02 = 150Ω.
Voltage Divider: Determine output voltage or component values in voltage divider circuits. Ohm's law helps understand how voltage divides across resistors.
Power Supply Design: Calculate current draw and power requirements for circuits. This helps select appropriate power supplies and ensure components can handle the power.
Component Sizing: Determine appropriate resistor values for current limiting, pull-up/pull-down resistors, and signal conditioning circuits.
Tips for Accurate Results
- Enter at least 2 values to calculate the remaining values
- Use consistent units (volts, amperes, ohms, watts)
- Ohm's law applies to DC circuits and resistive AC circuits
- For reactive components (inductors, capacitors), use impedance instead of resistance
- Power calculations assume resistive loads
- Always verify component ratings (power, voltage, current) match calculated values
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 a fundamental relationship in electrical circuits that describes how voltage, current, and resistance are related.
When does Ohm's law apply?
Ohm's law applies to DC circuits and resistive AC circuits. For reactive components (inductors and capacitors), you need to use impedance instead of resistance. Ohm's law is most accurate for linear, resistive elements.
How do I calculate power?
Power can be calculated using: P = V × I, P = I² × R, or P = V² / R. If you know any two of voltage, current, and resistance, you can calculate power using these formulas.
Can I use this for AC circuits?
For purely resistive AC circuits, yes. For circuits with inductors or capacitors, you need to use impedance (Z) instead of resistance (R), and consider phase relationships. This calculator is primarily for DC or resistive circuits.
What if I enter all 4 values?
If all values are entered, the calculator will verify they satisfy Ohm's law relationships. If they don't match, it will calculate the correct values based on the most reliable inputs (typically voltage and current).