i was able to find this though

The reference point for the threshold of hearing, equal to 20 microPA (micro Pascals rms). Since 1 PA = 1 newton/m2 = .000145 PSI (pounds per square inch). Then 0 dB-SPL = 2.9 nano PSI (rms) -- an unbelievably small value. This means that since 1 atm = 14.7 PSI, it is equivalent to a loudness level of 194 dB-SPL!