# Atmospheric pressure 1Atm or 100 kPa?

## Main Question or Discussion Point

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?

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mgb_phys
Homework Helper
it depends who you work for !!!
IUPAC use 100Kpa but NIST use 101.3Kpa, as do most ISO standards.

None of these change the fact that the average air pressure is 101.3kpa

ok. average atmospheric pressure = 1 Atm and that's that. Good enough for now. I'll let them be confused later.

Borek
Mentor
Using Atm allows me to compare 1Atm to 4.5 Atm at the bottom of a local lake and 3,000,000 Atm at the core.

Borek
Mentor
Could be a good point, but... where do you get 4.5 atm from?

Could be a good point, but... where do you get 4.5 atm from?
It's a local lake. I calculated it myself from the depth.

Borek
Mentor
So I guess lake is 45 m deep?