We have answered your question.
Doing the math, (W=VA) depending on color they will usually be in the 0.04-0.09 watt range.
Watts is equal to Volts times Amps (W=VA). As we said. These leds are rated at 20mA. The forward voltage (V) depends on the color of the led.
The tutorial describes all of this in great detail. It also tells you exactly which resistors you need to use.