Calculate electrical power dissipation from voltage, current, and resistance using the standard formulas P = VI, P = I²R, and P = V²/R. Enter any two known electrical values and this calculator determines the missing quantity and power in watts.
Enter any two known values. Leave the unknown value empty and the calculator will determine it.
When voltage and current are known, multiply the voltage in volts by the current in amperes. The result is power in watts.
If current and resistance are known, square the current and multiply it by resistance. This formula is especially useful for resistor power calculations.
When voltage and resistance are known, square the voltage and divide it by the resistance.
Electrical power is directly related to voltage, current, and resistance. Because these quantities are connected by Ohm's Law, power can be calculated in several equivalent ways.
Enter any two known values among voltage, current, and resistance.
The calculator selects the appropriate power and Ohm's Law relationship.
The resulting electrical power is shown in watts together with all three values.
Suppose a resistor has 12 V across it. We can calculate its current and power.
| Quantity | Calculation | Result |
|---|---|---|
| Voltage | Given | 12 V |
| Resistance | Given | 24 Ω |
| Current | 12 / 24 | 0.5 A |
| Power | 12 × 0.5 | 6 W |
The same result can be obtained directly from P = V²/R: 12² / 24 = 6 W.
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Power dissipation is the rate at which electrical energy is converted into another form, commonly heat in a resistor. It is measured in watts (W).
The main formulas are P = V × I, P = I² × R, and P = V² / R, where P is power in watts, V is voltage in volts, I is current in amperes, and R is resistance in ohms.
Use P = V² / R. Divide the square of the voltage across the resistor by its resistance in ohms.
Use P = I² × R. Square the current in amperes and multiply it by the resistance in ohms.
A resistor should normally have a power rating higher than its expected operating dissipation. Designers commonly include a safety margin rather than operating a resistor continuously at its maximum rating.
Yes. Enter any two of voltage, current, and resistance. The calculator determines the missing electrical quantity and the resulting power dissipation.