With the recent addition of new missions, people are posting skill gains from rewards. As the amount gained depends on your initial level, its more useful to look at the TT value of the reward. A tool to achieve that is at http://www.entropedia.info/SkillCalc.aspx At the top of the page fill in the following fields: Start Skill Level - your skill before you accept the reward End Skill Level - your skill after you accept the reward Then click on the Implant Button. It will tell you the TT value of the esi that would be required to implant the skill. Alternatively, if you know what the reward is and want to find out how much skill you will gain, you can instead fill in Start Skill Level, Chip TT value and click Implant to find out what your end skill should be. One disclaimer, the tool gives crazy results for skills over 10k. No, I don't know the exact formula used. Ican't find the referenced forum thread.
Agree with Snape, excellent tip. Here is another one, if you want to calculate your total skills check out this tool: Skill Scanner And then you could also use this tool to calculate how to chip in or out skills to get to a certain level or unlock a certain skill: Chipping Optimizer