Resistor Wattage Calculator
Compute power and choose a safe wattage rating
How to Use This Calculator
1
Enter Voltage
Provide the voltage across the resistor in volts (V).
2
Enter Resistance
Provide the resistance in ohms (Ω).
3
Calculate and Pick Rating
Use the recommended wattage (≥2×) or the next higher standard rating.
Formula
P = V² / R
P = I² R
P = V I
Choose the form that matches known quantities. This tool uses P = V²/R.
About Resistor Wattage
Resistors dissipate heat proportional to electrical power. Selecting a wattage rating with margin improves reliability and reduces temperature rise.
- Use ≥2× safety for steady loads; higher for pulses.
- Check derating curves for elevated ambient temperatures.
- Consider resistor package and airflow.
Frequently Asked Questions
Can I enter current instead?
This version uses voltage and resistance. Use Ohm’s law (I = V/R) then P = I²R if needed.
Is 2× margin always enough?
For continuous DC loads, 2× is common. For pulsed or high ambient conditions, use higher margins.