Ohm's Law Calculator
Ohm's law states V = I × R; with P = V × I, any two of voltage, current, resistance and power give the other two. For example 12 V across 4 Ω drives 3 A and dissipates 36 W.
Enter any two values; the other two are calculated. The two fields you edited last are the inputs.
V = 12 V, I = 3 A, R = 4 Ω, P = 36 W
Ohm's Law Formulas
| Find | From V, I | From V, R | From I, R | From P, … |
|---|---|---|---|---|
| V | — | — | I × R | P / I, √(P R) |
| I | — | V / R | — | P / V, √(P / R) |
| R | V / I | — | — | V² / P, P / I² |
| P | V × I | V² / R | I² × R | — |
Worked Examples
- LED series resistor: 5 V supply, 2 V LED drop, 20 mA → R = (5 − 2) / 0.02 = 150 Ω, dissipating 3 × 0.02 = 0.06 W.
- Heater: 2000 W at 230 V → I = 2000 / 230 = 8.70 A, R = 230² / 2000 = 26.45 Ω.
- Wire loss: 10 A through 0.05 Ω → P = 10² × 0.05 = 5 W, voltage drop 0.5 V.
Frequently asked questions
What is Ohm's law?
For a resistor, voltage equals current times resistance: V = I × R. Combined with P = V × I it gives P = I²R and P = V²/R.
How much current does a 60 W bulb draw at 120 V?
I = P / V = 60 / 120 = 0.5 A, and its hot resistance is V / I = 240 Ω.
Does Ohm’s law apply to LEDs and motors?
Not directly. LEDs, diodes and motors are non-linear; Ohm’s law gives their instantaneous V/I ratio but not a constant resistance. It holds well for resistors and conductors at constant temperature.
Sources
- The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures .
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). Ohm's Law Calculator. Retrieved October 17, 2026, from https://scientificconverters.com/calculators/ohms-law/
IEEE
Scientific Converters, "Ohm's Law Calculator," scientificconverters.com. Accessed: Oct. 17, 2026. [Online]. Available: https://scientificconverters.com/calculators/ohms-law/