O2 (Oxygen) Molar Mass (With Calculations)

O2 (Oxygen) Molar Mass

Molar mass of O2 is 31.999 g/mol.

Well, now you have come to know the molar mass of O2.

But how can you get this value?

Let me show you the calculation to get the molar mass of O2 (Oxygen).

If you are a visual learner like me, then here is a short one minute video for you.

O2 Molar Mass Calculation

If you have a periodic table with you, then you can easily calculate the molar mass of O2 (Oxygen).

Because the molar mass of any molecule (or compound) can be calculated by simply adding the molar masses of individual atoms.

Now here we have to find the molar mass of O2 (Oxygen).

So for that, have a look at the periodic table given below.

You can see the molar mass value of all the atoms from this periodic table.

Now in O2, there are 2 Oxygen atoms.

So let’s look at the molar mass of Oxygen from the above periodic table.

You can see that;

The molar mass of Oxygen is 15.999 g/mol. [1]

Now, to calculate the molar mass of O2, you just have to add the molar mass of all the individual atoms that are present in O2.

You can see that in O2, there are 2 Oxygen atoms.

So, Molar mass of O2 = Molar mass of 2 Oxygen (O) atoms.
= (15.999) 2
= 31.998 g/mol

Hence the Molar mass of O2 is 31.998 g/mol.

I hope you have understood the short and simple calculation for finding the molar mass of O2.


  • In some books, you may see the unit of molar mass as grams/mole or g/mole. But all these units (i.e g/mol, grams/mole and g/mole) are the same. 
  • Always follow the calculation order to avoid any mistakes in calculation. First solve the brackets, then multiplications and at last do the final addition.
  • And don’t forget to put the unit g/mol to your final calculated molar mass.

Check out other related topics for more practice;
HCl (Hydrochloric acid) Molar Mass
H2 Molar Mass
Ethanol (C2H5OH) Molar Mass
NH3 (Ammonia) Molar Mass
CaCl2 (Calcium chloride) Molar Mass


Jay is an educator and has helped more than 100,000 students in their studies by providing simple and easy explanations on different science-related topics. With a desire to make learning accessible for everyone, he founded Knords Learning, an online learning platform that provides students with easily understandable explanations.

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