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Calculadora de la Ley de Ohm (V, I, R, P)

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Ohm’s Law Calculator

Calculate voltage, current, resistance, and power instantly. Enter any two of the four electrical values — the calculator solves for the remaining two using Ohm’s Law (V=IR) and the power equation (P=VI). Supports unit prefixes from micro to mega for real-world engineering use.

Cómo utilizar

Enter any two values — Voltage (V), Current (I), Resistance (R), or Power (P) — and the calculator instantly computes the other two. Select unit prefixes (mA, kΩ, mW, etc.) from the dropdown next to each input. Use preset buttons for common circuits like LED, USB, car battery, or household power. Results update in real-time as you type, with the formulas used shown in the output.

Características

Any-Two-In, Two-Out Solving — Enter any combination of two values (V+I, V+R, V+P, I+R, I+P, R+P) and get the remaining two calculated instantly.
Unit Prefix Support — Select from µA to A, mΩ to MΩ, µW to kW, mV to kV. Results auto-format to the most readable prefix.
Visualización de fórmulas — Shows which formula was used (V=IR, P=VI, P=I²R, P=V²/R) and the calculation steps so you can verify the math.
Quick Presets — Common circuit scenarios: LED circuit (5V/20mA), USB (5V/500mA), car battery (12V/10A), household mains (230V/10A).
Smart Input Tracking — Visual distinction between user-entered values and calculated results. Editing a third field automatically drops the oldest input.
Validación de Entrada — Prevents negative values and warns on extreme or unrealistic combinations.

Ohm’s Law Formulas

Ohm’s Law and the power equation give us 12 formulas linking V, I, R, and P. Given any two, the other two can be derived:

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V = I × R — Voltage equals current times resistance
I = V / R — Current equals voltage divided by resistance
R = V / I — Resistance equals voltage divided by current
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

 Preguntas frecuentes

What is Ohm's Law?

Ohm's Law states that the voltage (V) across a conductor is equal to the current (I) flowing through it multiplied by its resistance (R): V = I × R. Discovered by Georg Simon Ohm in 1827, it is the fundamental relationship in electrical engineering. Combined with the power equation (P = V × I), it allows you to calculate any two of the four electrical quantities (voltage, current, resistance, power) when the other two are known.
What units are used in Ohm's Law?

Voltage is measured in volts (V), current in amperes or amps (A), resistance in ohms (Ω), and power in watts (W). In practice, you'll often work with prefixed units: milliamps (mA) for small currents, kilohms (kΩ) for larger resistances, milliwatts (mW) for low-power circuits, and so on. This calculator handles all common prefixes automatically.
How do I calculate the resistor needed for an LED?

To find the resistor for an LED: subtract the LED's forward voltage from the supply voltage, then divide by the desired current. For example, with a 5V supply, a red LED (2V forward voltage), and 20mA target current: R = (5V - 2V) / 0.020A = 150Ω. Use this calculator by entering the voltage across the resistor (supply minus LED voltage) and the desired current to find the resistance and power dissipation.
Why do I only need to enter two values?

Ohm's Law (V=IR) and the power equation (P=VI) together contain four variables linked by two independent equations. With two equations and four unknowns, you need exactly two known values to solve for the remaining two. Any combination of two inputs works — the calculator selects the appropriate formula chain automatically.