If you don't have a calculator handy, use this JavaScript resistor calculator to do the math.
Source Voltage
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LED Forward Voltage Drop
LED Forward Current in Milliamps
Needed Resistance in Ohms
Using Closest Standard 5% Resistor
Closest Standard 5% Resistor
Closest Standard 5% Resistor Wattage
Actual Current
Actual Power Dissipated By LED
Actual Power Dissipated By Resistor