Ohm’s Law Calculator
Solve for Voltage ($V$), Current ($I$), Resistance ($R$), or Power ($P$) by entering any two known parameters with step-by-step formula proofs and interactive Ohm's Law identity wheel diagrams.
Enter Any 2 Parameters
Step-by-Step Ohm's Law & Joule's Law Derivation
How to Calculate Ohm's Law (V, I, R, P)
Ohm's Law defines the relationship between Voltage (V), Current (I), and Resistance (R): V = I × R. Joule's Law defines Electrical Power: P = V × I = I²R = V²/R. Enter any two known circuit values to calculate the remaining two instantly.
Ohm’s Law Definition & The Hydraulic Circuit Analogy
Discovered in 1827 by German physicist Georg Simon Ohm, Ohm’s Law defines the fundamental proportional relationship governing direct current electrical circuits:
Electrical potential pressure driving charge
Rate of electrical charge flow (Coulombs/sec)
Material opposition to charge flow
The 12 Ohm’s Law & Joule’s Power Formulas
| To Find | Formula 1 | Formula 2 | Formula 3 |
|---|---|---|---|
| Voltage (V) | V = I · R | V = P / I | V = √(P · R) |
| Current (I) | I = V / R | I = P / V | I = √(P / R) |
| Resistance (R) | R = V / I | R = V² / P | R = P / I² |
| Power (P) | P = V · I | P = I² · R | P = V² / R |
Real-World Applications of Ohm’s Law
LED Current-Limiting Resistors
Circuit designers calculate ($R = (V_{\text{supply}} - V_{\text{forward}}) / I$) to prevent light-emitting diodes from burning out under excess current.
Household Breaker Sizing
Electricians sum total appliance wattage ($P/V = I$) to ensure circuit draw does not exceed 15A or 20A branch breakers.
Audio Speaker Impedance
Car and home audio engineers match 4Ω and 8Ω speaker loads to amplifier voltage rails ($P = V^2 / R$) for clean audio power delivery.
Step-by-Step Worked Numerical Solutions
Problem: A 12V battery delivers 2.5 Amps to a DC motor. Find the resistance and power output.
Common Pitfalls & Mistakes
Milliamps to Amps Conversion
Forgetting that 20 mA = 0.02 A results in calculations off by a factor of 1,000.
Resistor Power Dissipation Rating
Selecting the right resistance value is useless if actual power dissipation exceeds the component's 1/4W or 1/2W thermal rating.
Applying to Non-Ohmic Diodes
Semiconductor PN junctions have dynamic non-linear resistance that cannot be modeled by simple static Ohm's Law.
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