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Enter any two of voltage, current, resistance and power to get the other two, with units from µA to kV and mΩ to MΩ.
Also covers: Voltage calculator · Current calculator · Resistance calculator · V = IR
Voltage
12 V
Current
54.545455 mA
Resistance
220 Ω
Power
654.54545 mW
Working
A resistor dissipating 0.65454545 W needs a power rating above that — common through-hole resistors are rated ¼ W, so pick a larger rating with margin (often 2×).
Voltage, current, resistance, or power, each in the unit you like.
With the formulas used.
V = I × R: the voltage across a resistor equals the current through it times its resistance.
Subtract the LED's forward voltage from the supply voltage, then divide by the LED current. For 5 V, a 2 V LED and 20 mA: (5 − 2) ÷ 0.02 = 150 Ω.
For resistive loads, yes (using RMS values). Motors and other inductive loads also need the power factor.
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