Enter any two of Voltage, Current, or Resistance into the Resistor Wattage Calculator, and it works out your Power Dissipated along with a Recommended Wattage Rating — so you know exactly which resistor can handle the heat without burning out.
Power Dissipated
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Recommended Wattage Rating
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Calculated Voltage
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Calculated Current
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Calculated Resistance
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Calculate the power dissipation using P = V²/R, P = I²R, or P = VI. Then choose a resistor with a wattage rating at least 2x higher than the calculated power for safety margin and reliability.
There are three formulas: P = V²/R (voltage and resistance), P = I²R (current and resistance), and P = VI (voltage and current). Use whichever formula matches the values you know.
Using a safety margin (typically 2x the calculated power) ensures the resistor doesn't overheat, extends its lifespan, and maintains stable performance under varying conditions.
This calculator is primarily designed for DC circuits. For AC circuits, you need to consider RMS values and additional factors like reactive power and power factor.
A resistor with insufficient wattage rating will overheat, potentially burn out, change resistance value, or even cause circuit failure. Always use appropriate safety margins.
Power dissipation is inversely proportional to resistance when voltage is constant (P = V²/R), but directly proportional when current is constant (P = I²R).
Common ratings include 1/8W, 1/4W, 1/2W, 1W, 2W, 5W, 10W, and higher. Choose based on your calculated power requirements with appropriate safety margin.
No, resistors consume power and convert it to heat. They cannot supply power to other components - they only dissipate energy from the circuit.