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Molecular Weight Calculator

Created by Łucja Zaborowska, MD, PhD candidate
Reviewed by Bogna Szyk and Jack Bowater
Last updated: May 16, 2024

The molecular weight calculator is a simple tool that can be used to compute the mass of a given molecule without using the periodic table of elements.

In this article, we won't be only talking about finding molecular weight - we'll also focus on theory, atomic mass, and the molecular mass calculation formula.

How to use the molecular weight calculator?

All you need to know to use our molecular weight (MW) calculator is the chemical formula of the particle you want to calculate.

  1. Choose the first element of your chemical formula.

  2. Enter how many of that atom it has.

  3. Repeat the process as many times as you need to complete your formula! Your results will be shown in unified atomic mass units, [u] = [Da] (daltons).

Both the MW and the chemical formula are displayed at the bottom of our MW calculator. ⚛️

Hey, do you already know the difference between molarity and molality? Learn more about them in the molality calculator and molarity calculator. 🤔

Molecular weight vs. molar mass

While it may seem that both of these names are synonyms - it's not entirely true. Even though they usually have identical values, they mean different things.

  1. Molecular weight/ molecular mass describes the mass of a single molecule of a substance given in daltons (Da) or u.

    • Molecular mass of water: 18 u.
  2. Molar mass is the mass of 1 mole of a substance, given in g/mol. 1 mol consists of exactly 6.02214076 * 10²³ molecules.

    • Molar mass of water: 18 g/mol.

Get to know some more with our variety of mole-related tools like this molar mass of gas calculator or the percentage concentration to molarity calculator.

How to calculate molecular weight?

Try it yourself! We know that our ready-to-go formula mass calculator is the easiest solution - nevertheless, we'd like to show you how we made it.

  1. Let's focus on a simple task: How to calculate molecular mass of glucose?

  2. Find the chemical formula of the glucose.

    • C₆H₁₂O₆
  3. Transform the formula:

    MW = (6 * C) + (12 * H) + (6 * O)


    • MW - molecular weight;
    • C - atomic mass of carbon;
    • H - atomic mass of hydrogen; and
    • O - atomic mass of oxygen.
  4. Find your elements in the periodic table of the elements. The atomic mass is usually shown below the symbol of the element.

    • C - 12 u;
    • H - 1 u; and
    • O - 16 u.
  5. Input the values into the molecular weight equation and calculate the result:

    MW = (6 * 12u) + (12 * 1u) + (6 * 16u),

    MW = 180 u

✅ We got the right answer - the molecular weight of glucose is equal to 180 u.

Periodic table of elements - curiosities

The periodic table of elements, also called the Mendeleev table, contains 118 elements. The last 4 of them were added in 2016 - no wonder why some of us still remember its older version, filled with the then-unknown Uuu elements.

The periodic table contains 4 elements named after American people or places in the US:

  • 103 - Lawrencium — named after Ernest Lawrence, inventor of the cyclotron;

  • 106 - Seaborgium — named after nuclear chemist Glenn T. Seaborg;

  • 117 - Tennessine — named after the state; and

  • 98 - Californium — named after the state.

We can't forget that many Noble Prize winners of other nationalities also lived and worked in the USA, including German Albert Einstein (Einsteinium, 99) and Italian Enrico Fermi (Fermium, 100).

💡 Contrary to a popular belief, Americium was named after both American continents.

Go ahead and look them up in our atomic weight calculator!

Łucja Zaborowska, MD, PhD candidate
Related calculators
1st Element
Hydrogen (H)
No. of atoms
2nd Element
No. of atoms
Your molecule:
Molecular weight: 1 u.
Chemical formula: H
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