i have a stock turbo boost gauge on my wrx and its in mpa how would i be able to read it in psi?

 

There are a number of conversion charts posted online, you can search for them.
Briefly though, the important numbers you need to know are that .05 mPa = about 7psi, and .1 mPa = about 14 psi.
On a stock WRX you can expect to see around .05 at moderate throttle in the mid-RPM range, and up to around .09 at heavier throttle.
When idling, coasting/decelerating or crusing at steady light throttle you will see vacuum. Normal vacuum at idle is about -.06 to -.07. You'll see it change with varying engine loads such as the AC cycling on and off.

 

http://www.chapelsteel.com/mpa-psi.html

they have a conversion table. wrx is 13.5 psi or .09Mpa