Figuring Out Percentiles when Mean & Std Dev are Known

I'm trying to figure out in excel how to figure out a percentile when Mean and Standard Deviation are known. The problem with Excel is that it doesn't give you the option of calculating the percentile of a number. The only option seems to be specifying what percentile a certain array is in. Additionally, I don't have an array of numbers.

So, I know:
mean = 100
Standard Deviation = 15

If I come up with a score of say 65 - what percentile does that fall in?

Thanks so much!

[attachment=0:1t6zugqt]PR_and_NCE.gif[/attachment:1t6zugqt]If you are dealing with data considered to be "normally distributed",
You convert your score to a z-score using

z=(x-mean)/(standard deviation)

z=(65-100)/(15) = -35/(15) = -2.3 approximately.

This z-score references the number of standard deviations your score is from the mean.

You can read off the percentile rank from that.

In this case, it corresponds to lower 1% .