Figuring out where your handlebar is going to end up after swapping stems can be a pain.  To make it easier, you can use this stem calculator to get exact figures before you make the swap.

I found this on MTBR.com way back, posted in this thread by Squash.

Download the ZIP file, and you’ll find two files inside.  One is a .doc file explaining how to use the calc, and the other is a spreadsheet where you’ll do your work.

http://gearinches.com/misc/stem-calc.zip

Here’s another one that may be even easier to use, but it’s online only:
http://www.brightspoke.com/t/bike-stem-calculator.html

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