Ignoring normal variations, I've always been told that atmospheric pressure is... 1 Atm = 101,325 Pa However, Wikipedia says atmospheric pressure was re-defined in 1999 to be exactly 100 kPa. This would mean that atmospheric pressure is now 0.98692 Atm. http://en.wikipedia.org/wiki/Atmospheric_pressure I'm writing a lab activity for high school students. From what I've read, it seems that both conventions are used. Which convention should be used?