Ohm's Law Calculator
Calculate voltage, current, resistance, and power using Ohm's Law. Enter any two values to find the missing electrical parameters for your circuits.
Electrical Parameters
Common Circuit Examples
Ohm's Law Formulas
Calculated Results
Circuit Representation
How to Use the Ohm's Law Calculator
To use this calculator effectively:
- Enter any two known values (voltage, current, resistance, or power)
- Select appropriate units for current, resistance, and power
- Click "Calculate Missing Values" to find the unknown parameters
- The calculator will automatically determine which values to calculate
- Use the "Clear" buttons to remove individual values or "Clear All" to start over
- Try the preset examples to see common circuit scenarios
Understanding Ohm's Law
Ohm's Law describes the relationship between voltage, current, and resistance in electrical circuits:
Basic Formula: V = I × R
- V (Voltage): The electrical potential difference measured in volts (V)
- I (Current): The flow of electric charge measured in amperes (A)
- R (Resistance): The opposition to current flow measured in ohms (Ω)
Power Calculations
Power represents the rate of energy consumption and can be calculated using:
- P = V × I: Power equals voltage times current
- P = I² × R: Power equals current squared times resistance
- P = V² / R: Power equals voltage squared divided by resistance
Example: LED Circuit Calculation
Given: 5V power supply, 220Ω current-limiting resistor
Find: Current through LED and power dissipated by resistor
Solution:
- Current: I = V / R = 5V / 220Ω = 0.023A = 23mA
- Power: P = V² / R = 5² / 220 = 0.114W = 114mW
Result: The LED will receive 23mA of current, and the resistor will dissipate 114mW of heat.
Frequently Asked Questions
When does Ohm's Law apply?
Ohm's Law applies to linear, passive components like resistors at constant temperature. It doesn't directly apply to non-linear components like diodes, transistors, or components with varying resistance.
What's the difference between AC and DC calculations?
This calculator works for DC circuits and AC circuits with purely resistive loads. For AC circuits with reactive components (capacitors, inductors), you need to consider impedance instead of resistance.
How do I choose the right resistor power rating?
Choose a resistor with a power rating at least 2x higher than the calculated power dissipation. For example, if a resistor dissipates 0.25W, use a 0.5W or 1W rated resistor for safety.