LED current limiting resistor calculator

Calculates a current limiting resistor for LEDs.

Example 1: Must calculate the resistor for a led string of 4 green 5mm leds and 12V supplyView example
Supply voltagevolts
Target currentamperes
Led color 
Leds in seriespcs
E-series 
Results
Total voltage drop in leds2 volts
Required resistor500 ohms
Nearest resistor in E-series560 ohms
Resistor power loss~178.571429 milliwatts
Current with selected resistor~17.857143 milliamperes