# How many water molecules in the air - is my calculation correct?

I want to know how many water molecules are in one cubic meter of air (Relative humidity=20%, Temperature=293K)

This is my calculation:

$p=2.3kPa$ (because of vapor pressure at 20C is 2.3 kPa (as on wikipedia https://en.wikipedia.org/wiki/Vapour_pressure_of_water)

$pV=nRT$

$n=pV/RT$

Now I multiply n by $N_A$ and then by 0.2 (because relative humidity is 20%)

Is my approach reasonable?

• Why would you think it wouldn't be? – Chet Miller Jan 30 '17 at 12:50
• @ChesterMiller Because sometimes I'm stupid. And I have never done such calculations before. Maybe I'm missing something. – user46147 Jan 30 '17 at 14:58
• Nope. You're not missing anything. – Chet Miller Jan 30 '17 at 15:58