Instantly calculate molar mass and molecular weight for any chemical formula. Use our free molar mass calculator to get accurate g/mol values for chemistry homework, lab work, and stoichiometry.
Molar Mass Calculator
Enter a chemical formula and get the molar mass in g/mol with a full element breakdown.
Quick Element Selector
Click elements to build formula (Swipe left/right)
Row 1
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Row 6
Molar mass
18.015 g/mol
Element
Atomic #
Count
Atomic Mass
Contribution
Percent
What Is Molar Mass?
Molar mass is the mass of one mole of a compound, expressed in grams per mole (g/mol). It is the sum of the atomic masses of every atom in a molecule and is a key value in chemistry because it connects atomic-scale formulas to measurable mass. It is the essential factor used in our
grams to moles calculator
and its reverse, the
moles to grams converter
.
For most chemistry problems, molar mass and molecular weight are used interchangeably, but molar mass is the correct term for the mass of one mole of substance. Once you have the molar mass, you can also determine the number of particles in a sample by using the
moles to molecules calculator
or go deeper into individual atomic counts with the
moles to atoms calculator
.
Term Definitions
Atomic Weight
Atomic weight (relative atomic mass) is the weighted average mass of the atoms in a naturally occurring sample of an element. It is dimensionless, but chemists use it to calculate molar mass because it corresponds closely to grams per mole.
Molecular Weight
Molecular weight is the mass of a single molecule expressed in atomic mass units. For practical chemistry problems, molar mass in g/mol is usually the preferred measure, but the two are numerically similar.
Mole
A mole is a counting unit in chemistry equivalent to 6.022 × 10
23
particles. One mole of a compound contains Avogadro’s number of molecules, making molar mass the bridge between the atomic scale and the laboratory scale.
How to Calculate Molar Mass
To calculate molar mass, count the atoms in the formula, find each element's atomic mass, multiply by the number of atoms, and add the results.
M = Σ (atomic mass × atom count)
Molar Mass Formula Example
For water (H
2
O):
2 × 1.008 (H) + 1 × 15.999 (O) = 18.015 g/mol
For a compound with parentheses, treat the grouped atoms as a unit and multiply by the coefficient outside the parentheses.
Molecular Weight vs Molar Mass
Molecular weight is the mass of one molecule in atomic mass units (amu). Molar mass is the mass of one mole of molecules in grams per mole (g/mol). They are often used together in calculators because they share the same numeric result for most compounds in chemistry.
Visual Molar Mass Diagram
3D-style visual:
Molar mass connects atoms and their mass contributions into one mole.
How Formulas Work
List each element in the chemical formula.
Count the number of atoms for each element.
Multiply each atom count by the element’s atomic mass.
Add the results to get the compound’s molar mass.
Step-by-Step Molar Mass Examples
Example 1: Water (H
2
O)
H
2
O contains 2 hydrogen atoms and 1 oxygen atom.
These common compounds help you compare typical molar masses and learn how formula complexity affects result values.
Compound
Formula
Molar Mass (g/mol)
Water
H
2
O
18.015
Carbon dioxide
CO
2
44.009
Sodium chloride
NaCl
58.443
Glucose
C
6
H
12
O
6
180.156
Sulfuric acid
H
2
SO
4
98.079
Calcium hydroxide
Ca(OH)
2
74.092
Ammonia
NH
3
17.031
Why Molar Mass Matters
Molar mass is essential for stoichiometry, solution preparation, and converting between grams and moles. It tells you how much one mole of a substance weighs so that you can measure the right amount of reactant or product in a chemical reaction.
Knowing molar mass helps you prepare solutions with the correct concentration, work through limiting reagent problems, and compare molecular formulas in meaningful ways.
Use this calculator with formulas from your homework and lab notes. If you want a quick review, try these practice prompts:
What is the molar mass of ethanol (C
2
H
5
OH)?
Calculate the molar mass of sodium sulfate (Na
2
SO
4
).
Find the molar mass of glucose and compare it to the mass of one mole of carbon dioxide.
Practice Tip
Write the formula clearly, count each atom, then enter it exactly into the calculator. The correct capitalization of element symbols is essential.
Frequently Asked Questions
What is the difference between molar mass and molecular weight?
Molar mass is the mass of one mole of a substance, measured in g/mol. Molecular weight is the mass of a single molecule expressed in atomic mass units. For most chemistry tasks, the numeric results are treated as equivalent.
How do I use this molar mass calculator?
Enter any chemical formula using correct capitalization, then click Calculate. The calculator returns the total molar mass and shows each element's contribution in the breakdown table.
What units are used for molar mass?
Molar mass is expressed in grams per mole (g/mol), which is the standard unit used in chemistry for converting between substance mass and moles.
Can this calculator handle hydrates and parentheses?
Yes. The calculator supports formulas with parentheses, hydrate notation using *, and standard chemical formulas such as Ca(OH)
2
and CuSO
4
*5H
2
O.
Why should I use molar mass when studying chemistry?
Understanding molar mass makes chemical calculations consistent and reliable. It is the foundation for converting between mass and amount of substance, which is central to stoichiometry, titrations, and concentration calculations.