<p>The atmosphere is 20.95% Oxygen by volume, on a dry basis (i.e. without any water vapor).  See <a href="http://www.atmo.arizona.edu/students/courselinks/fall16/atmo336/lectures/sec1/composition.html" rel="nofollow noreferrer">here</a> for detailed composition information.</p>
<p>Your second question, how is the oxygen percentage calculated, is misguided I believe.  The composition of the atmosphere is measured with gas analyzers, not calculated.</p>

CC BY-SA 4.0
2024-01-07T02:26:52.210Z
Thank you for considering my questions and answering them, I appreciate it!
SPANDAN DASH
CC BY-SA 4.0
2024-01-06T03:31:46.330Z
2024-01-06T03:31:46.330Z
Mark
<p>The percentage of oxygen in the atmosphere is 21 percent, according to NASA.gov. I was trying to make a mathematical calculation about oxygen consumption of humans, when I realised that there is a gap in my understanding of the above mentioned fact. Is 21% of the MASS of the atmosphere that of oxygen, or is 21% of the VOLUME of the atmosphere that of oxygen? The mass is not evenly distributed in the atmosphere, and the volume of it is fixed. And for that matter, I have another question, how exactly is the percentage of oxygen in the atmosphere calculated?</p>

CC BY-SA 4.0
2024-01-07T07:17:34.257Z
Oxygen can be "measured" indirectly using spectrometry and a set of known references with calibrated gas.  See the Scripps Program here: https://scrippso2.ucsd.edu/what-we-do.html
f.thorpe
<atmosphere><oxygen>
On the percentage of oxygen in the atmosphere
SPANDAN DASH
# On the percentage of oxygen in the atmosphere

(Asked by: username_0 on 2024-01-05)

The percentage of oxygen in the atmosphere is 21 percent, according to NASA.gov. I was trying to make a mathematical calculation about oxygen consumption of humans, when I realised that there is a gap in my understanding of the above mentioned fact. Is 21% of the MASS of the atmosphere that of oxygen, or is 21% of the VOLUME of the atmosphere that of oxygen? The mass is not evenly distributed in the atmosphere, and the volume of it is fixed. And for that matter, I have another question, how exactly is the percentage of oxygen in the atmosphere calculated?

**Tags:** atmosphere, oxygen

> **Comments:**
> **username_1**: Oxygen can be "measured" indirectly using spectrometry and a set of known references with calibrated gas.  See the Scripps Program here: https://scrippso2.ucsd.edu/what-we-do.html  

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## 1 answers

### Answer by username_2 on 2024-01-06. Score: 1 | Accepted answer

The atmosphere is 20.95% Oxygen by volume, on a dry basis (i.e. without any water vapor). See [here](http://www.atmo.arizona.edu/students/courselinks/fall16/atmo336/lectures/sec1/composition.html) for detailed composition information.

Your second question, how is the oxygen percentage calculated, is misguided I believe. The composition of the atmosphere is measured with gas analyzers, not calculated.

> **Comments:**
> **username_0**: Thank you for considering my questions and answering them, I appreciate it!  

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