What Is Molar Mass and How Is It Calculated?
Molar mass is the mass of one mole (6.022 × 10²³ particles) of a substance, expressed in grams per mole (g/mol). It is calculated by summing the standard atomic weights of every atom in a compound's chemical formula, each multiplied by how many times that atom appears.
For a formula like C6H12O6 (glucose), the molar mass formula is: M = (6 × atomic weight of C) + (12 × atomic weight of H) + (6 × atomic weight of O). Atomic weights come from the periodic table published by IUPAC (International Union of Pure and Applied Chemistry), which standardizes conventional values for all 118 known elements.
According to IUPAC, the standard atomic weight of carbon is 12.011 g/mol and oxygen is 15.999 g/mol — values based on the natural isotopic abundance of each element, not a single isotope's exact mass.
How to Use This Molar Mass Calculator
Pick a common compound from the dropdown, or type any chemical formula directly, and the calculator instantly parses it into elements and sums their weighted masses.
- Common Compound: A shortcut list of frequently searched formulas — selecting one auto-fills the formula field.
- Chemical Formula: Type any valid formula using standard element capitalization (Na, not NA) and counts, e.g.
H2SO4orFe2O3. - Parentheses: Use them to group repeating atom clusters, such as the ammonium ion in
(NH4)2SO4, which the calculator expands correctly before summing.
Molar mass in g/mol is an SI-derived unit used identically in every country — there is no imperial equivalent to convert, so results are directly comparable across labs and textbooks worldwide.
Common Compound Molar Masses
The table below lists the molar mass of compounds students and lab technicians look up most often, each computed the same way this calculator computes any formula you enter.
| Compound | Formula | Molar Mass (g/mol) |
|---|---|---|
| Water | H2O | 18.015 |
| Carbon Dioxide | CO2 | 44.009 |
| Sodium Chloride | NaCl | 58.44 |
| Glucose | C6H12O6 | 180.156 |
| Sulfuric Acid | H2SO4 | 98.079 |
| Calcium Carbonate | CaCO3 | 100.087 |
Frequently Asked Questions
What is the molar mass of water (H2O)?
Water's molar mass is 18.015 g/mol — calculated as two hydrogen atoms (2 × 1.008) plus one oxygen atom (15.999), giving 2.016 + 15.999 = 18.015 g/mol.
How accurate is this molar mass calculator?
This calculator uses IUPAC standard atomic weights for all 118 elements, so results match textbook and lab reference values to three decimal places. It assumes the natural isotopic composition of each element; if you need a single-isotope exact mass for mass spectrometry, use a dedicated isotope mass table instead.
What is the difference between molar mass and molecular weight?
Molar mass and molecular weight describe the same quantity in practice — the mass of one mole of a substance in g/mol — though molecular weight is technically a dimensionless ratio (relative to 1/12 the mass of carbon-12) while molar mass carries explicit g/mol units.
How do I calculate molar mass from a chemical formula by hand?
List every element in the formula with its count, look up each element's atomic weight on the periodic table, multiply count by weight for each element, then add all the subtotals together — exactly the steps shown in this calculator's "How was this calculated?" breakdown.