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Ohm's Law Calculator
Enter any two of voltage, current, resistance, or power to calculate the other two.
Voltage (V)
—
Current (A)
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Resistance (Ω)
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Power (W)
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V = I × R | P = V × I = I²R = V²/R. Enter any two known values; the other two will be calculated.
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Common Values
| Component | Typical Voltage | Typical Current |
|---|---|---|
| USB port | 5V | 0.5–2A |
| AA battery | 1.5V | 0.5–3A max |
| Car battery | 12.6V | 200–600A (cranking) |
| Standard LED | 1.8–3.3V | 20mA |
| Arduino GPIO | 5V / 3.3V | 20–40mA max |
| US wall outlet | 120V AC | 15–20A circuit |
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Understanding Ohm's Law
Ohm's law is the foundation of electrical engineering. It describes the relationship between voltage (V), current (I), and resistance (R): V = I × R.
Power can be derived from any two of these values: P = V × I = I²R = V²/R. This calculator lets you enter any two known values and computes the remaining two.
This relationship holds for resistive (ohmic) loads. For reactive components like capacitors and inductors in AC circuits, impedance replaces resistance.