There are many sites that have simple calculators for LEDS and resistors
here is an example of one I find useful by Rob 'linear' Arnold.
simple one LED version -http://led.linear1.org/1led.wiz
multi LED version - http://led.linear1.org/led.wiz
* This calculator rounds the resistance up to the next standard resistor value. You should actually be able to buy a 5% resistor with the value returned by the calculator.
** Power calculations assume use of the standard value current-limiting resistor shown above. Resistor power ratings are chosen based on operating within 60% of the rated value.
LED calculator version 2.0 Copyright 2001-2006, Rob 'linear' Arnold. All rights reserved.