How this calculator works
Charge carriers transfer electrical energy to the resistor. At constant resistance, dissipated power is current squared times resistance, and energy is power multiplied by elapsed time. For AC, use RMS current when resistance is effectively constant. Temperature-dependent resistance or changing current requires integrating power over time; generated heat does not itself specify the final body temperature.
Formula
P = I²R; Q = I²Rt; I = sqrt[Q/(Rt)]; R = Q/(I²t); t = Q/(I²R).
Worked example
A 2 A current through 10 ohms for 60 s generates 2400 J at 40 W. A 3 A current through 4 ohms for 5 s generates 180 J at 36 W.
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Frequently asked questions
Should AC current be a peak value?
Use RMS current. A sinusoidal peak must be divided by the square root of two.
Does all heat stay in the resistor?
No. Energy may flow into its surroundings as it is produced.
Why is current returned as a magnitude?
Both current directions produce the same I squared and therefore the same heating.