H2O (Water) Molar Mass (With Calculations)

H2O (Water) Molar Mass

Molar mass of H2O (Water) is 18.015 g/mol.

Well, now you have come to know the molar mass of H2O.

But how can you get this value?

Let me show you the calculation to get the molar mass of H2O (Water).

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

H2O (Water) Molar Mass Calculation

If you have a periodic table with you, then you can easily calculate the molar mass of H2O (Water).

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 H2O (Water).

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 H2O, there are 2 Hydrogen atoms and 1 Oxygen atom.

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

You can see that;

The molar mass of Hydrogen is 1.008 g/mol. [1]

The molar mass of Oxygen is 15.999 g/mol. [2]

Now, to calculate the molar mass of H2O, you just have to add the molar mass of all the individual atoms that are present in H2O.

You can see that in H2O, there are 2 Hydrogen atoms and 1 Oxygen atom.

So, Molar mass of H2O = Molar mass of 2 Hydrogen (H) atoms + Molar mass of 1 Oxygen (O) atom.
= (1.008) 2 + 15.999
= 2.016 + 15.999
= 18.015 g/mol

Hence the Molar mass of H2O is 18.015 g/mol.

I hope you have understood the short and simple calculation for finding the molar mass of H2O.


  • 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;
O2 (Oxygen) Molar Mass
HCl (Hydrochloric acid) Molar Mass
H2 Molar Mass
Ethanol (C2H5OH) Molar Mass
NH3 (Ammonia) 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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