MulticalcOhm's Law Calculator
Calculate V, I, R, and P using Ohm's LawEnter any 2 values to calculate the other 2.
Ohm's Law Guide
What is Ohm's Law?
Ohm's Law describes the relationship between voltage, current, and resistance in an electrical circuit. It's one of the most fundamental principles in electronics and electrical engineering.
V = I × R
The Four Key Formulas:
- Voltage: V = I × R
- Current: I = V / R
- Resistance: R = V / I
- Power: P = V × I = I² × R = V² / R
Understanding the Variables:
- V (Voltage): Electrical potential difference measured in volts (V)
- I (Current): Flow of electric charge measured in amperes (A)
- R (Resistance): Opposition to current flow measured in ohms (Ω)
- P (Power): Rate of energy transfer measured in watts (W)
Common Applications
- LED Circuits: Calculate resistor values for LED current limiting
- Power Supplies: Determine voltage and current requirements
- Circuit Design: Size components for proper operation
- Troubleshooting: Diagnose electrical problems
Pro Tips
-
Units
Matter
Always use consistent units: volts, amperes, ohms, and watts. -
Series vs Parallel
Ohm's Law applies differently in series and parallel circuits. -
Real-World
Account for component tolerances and temperature effects.
Quick Examples
I = 12V / 4Ω = 3A
P = 12V × 3A = 36W
R = 2V / 0.02A = 100Ω
P = 2V × 0.02A = 0.04W
Frequently Asked Questions
A: Ohm's Law states that voltage equals current times resistance (V = I × R). It means that if you increase voltage, current increases proportionally (assuming resistance stays constant). If you increase resistance, current decreases.
A: Power can be calculated three ways: P = V × I (voltage times current), P = I² × R (current squared times resistance), or P = V² / R (voltage squared divided by resistance). Use whichever formula matches the values you know.
A: Use volts (V) for voltage, amperes or amps (A) for current, ohms (Ω) for resistance, and watts (W) for power. For small values, use milliamps (mA = A/1000), kilohms (kΩ = Ω×1000), or megohms (MΩ = Ω×1,000,000).
A: Ohm's Law works for AC circuits, but you must use impedance (Z) instead of resistance (R) for circuits with capacitors or inductors. For purely resistive AC circuits, it works the same as DC.
A: Use R = (V_source - V_LED) / I_LED. For example, with a 12V source, 2V LED, and 20mA current: R = (12V - 2V) / 0.02A = 500Ω. Use the next standard value (510Ω or 560Ω).
A: Exceeding voltage, current, or power ratings can damage or destroy components. Resistors overheat and burn out. LEDs fail permanently. Always stay within component specifications and add safety margins.
Disclaimer
Important Notice:
- This calculator provides theoretical calculations based on ideal conditions. Real-world circuits may behave differently due to component tolerances, temperature effects, and other factors.
- Always verify calculations and use appropriate safety margins when designing circuits. Component ratings should never be exceeded.
- Electrical safety: Working with electricity can be dangerous. High voltages and currents can cause serious injury or death. Always follow proper safety procedures.
- This tool assumes ideal components and DC circuits. AC circuits, especially with reactive components (capacitors, inductors), require additional considerations.
- Component power ratings must be respected. Calculate power dissipation (P = I² × R or P = V² / R) and ensure components can handle it.
- For precision applications, account for component tolerances (typically ±5% to ±20% for resistors) and temperature coefficients.
- This calculator is for educational purposes. For critical applications, consult with qualified electrical engineers and follow industry standards.
- Series and parallel circuit calculations require different approaches. This calculator assumes simple circuits with single components.
- We are not responsible for any errors, component damage, injuries, or other consequences resulting from the use of this calculator.
Always double-check calculations and follow proper electrical safety practices.
Ohm's Law Calculator
Calculate voltage, current, resistance, and power using Ohm's Law. Enter any 2 values to find the other 2!
Ohm's Law Triangle
Cover what you want to find:
V = I × R | I = V / R | R = V / I
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Did You Know?
Ohm's Law was formulated by German physicist Georg Ohm in 1827. It's one of the most fundamental laws in electrical engineering and is used billions of times daily in circuit design!