What do you mean NO2? Nitrogen dioxide or nitrite anion? For nitrite see the review

 Methods for the detection and determination of nitrite and nitrate: A review

https://doi.org/10.1016/j.talanta.2016.12.044

Selective electrode on NO2-. 

I have prepared a calculation method for you. 

Dear Mohammad, did you take into account that nitrous acid is  unstable in water?

thank you all for your responses!

dear Mohammad, as far as I'm concerned, the way HNO2 is computed differs from what you mentioned in your calculation. According to a wide variety of articles the concentration of HNO2 produced by NaNO2  is computed via below formula, and the reason why I wanted to measure the concentration of nitrite was to calculate HNO2 via this formula ( the reference has also been attached).

Article Inhibition of Nitrification by Ammonia and Nitrous-Acid

 Dear Seyed, 

First, your question is badly formulated and you did not reply to my request. 

Second, you seem to be interested in calculation of the equilibrium 

HNO2 = NO2(-) + H(+).  

This is a trivial task described in textbooks. In addition, there exist numerous softwares to calculate the distribution diagrams of equilibria. 

The right formula is 

[HNO2]/{[HNO2]+[NO2-]} = {10^(pKa-pH)}/{1 + 10^(pKa-pH)}, pKa of nitrous acid is 3.15

Keep i mind that nitrous acid is unstable in water

 dear yurii,

sorry, I answered but it seems that it wasn't sent. I apologize again. I meant nitrite anion not nitrogen dioxide.  actually, I know this is so unstable in aqueous environments, but my problem is that I don't have the concentration of nitrite anion stemming from NaNO2 added. lets put nitrous acid aside, what I actually need to know is that in the equilibrium of  NaNO2--->NA+ +NO2-  , can we calculate NO2- via molar mass ratio (stoichiometry)? in other words, is NaNO2 completely ionized in water (pH=7)?

thank you so much. 

Yes, NaNO2 is completely dissociated  in water unless you have > 0.5 M.