Last updated: March 2026
This Molecular Weight Calculator determines the molar mass and elemental percentage composition of any chemical compound. We built this tool to provide instant, precise stoichiometry data for students, researchers, and lab professionals working with complex chemical formulas.
Enter a chemical formula using standard case-sensitive periodic table notation (like H2O or C6H12O6). The tool maps each element to its standard atomic weight, multiplies by the atom count, and sums the total. It natively processes nested parentheses and common hydrate notations.
If you need to calculate solution concentration after finding molar mass, try our Molarity Calculator for accurate results.
To convert mass into moles for chemistry problems, use our Gram to Mole Calculator.
Explore more related tools in our Science Calculators section.
This calculator relies on standard IUPAC atomic weights based on the natural isotopic distribution found on Earth. It is highly accurate for general laboratory and educational use but cannot account for synthetically enriched isotopic samples required in specialized mass spectrometry.
Syntax Note: This calculator supports parentheses (), square brackets [], and hydrates separated by a dot . (e.g., CuSO4.5H2O). Please ensure element symbols are case-sensitive (e.g., use "Co" for Cobalt, not "co").
This guide explores the fundamentals of chemical mass calculations. Whether you are a chemistry student learning to balance your first equation or a technician preparing molar solutions, understanding how to find the mass of a compound is a core skill.
In standard laboratory environments, the terms "Molecular Weight" (MW) and "Molar Mass" (MM) are frequently used interchangeably. However, chemically speaking, they describe different scales.
Molecular weight represents the mass of a single molecule of a given substance. Because individual atoms are incredibly small, they are measured in the Unified Atomic Mass Unit (u), or the Dalton (Da).
Molar mass is the mass of one entire mole of a substance. A "mole" is a fixed quantity of particles defined by Avogadro’s Number (6.022 × 10²³). This is the practical unit used in stoichiometry because it connects microscopic atoms to macroscopic grams that can be weighed on a scale.
Knowing how to perform this calculation manually is vital for chemistry coursework. Let us look at a complex example: Calcium Phosphate, with the formula Ca3(PO4)2.
First, break the formula into individual elements. Pay attention to subscripts outside parentheses, as they act as a multiplier for everything inside the brackets.
Consult a periodic table for the average atomic mass of each element. (Values rounded here to 3 decimal places):
Multiply the count of each atom by its specific atomic weight, then add them together:
| Element | Count | Atomic Weight | Total Mass Contribution |
|---|---|---|---|
| Calcium | 3 | 40.078 | 120.234 |
| Phosphorus | 2 | 30.974 | 61.948 |
| Oxygen | 8 | 15.999 | 127.992 |
| Total | 310.174 g/mol |
Elements exist in nature as mixtures of isotopes—atoms that share the same number of protons but have different numbers of neutrons. For instance, natural Chlorine is approximately 75% Chlorine-35 and 25% Chlorine-37. The atomic weight shown on the periodic table is a weighted average of these naturally occurring isotopes, which is why the values are almost never whole numbers.
This calculation is standard for lab preparation. If an experimental procedure requires 0.5 moles of NaCl, you need to know how much to weigh out on a scale.
Formula: Mass (g) = Moles (mol) × Molar Mass (g/mol)
Using our calculator, NaCl is 58.44 g/mol. Calculation: 0.5 × 58.44 = 29.22 grams of NaCl.
If you synthesize an unknown compound, you can combust it to find the percentage of Carbon and Hydrogen by mass, then compare those percentages to theoretical values generated by this tool to verify the identity of the substance.
Here are the molar masses of frequently used chemicals for quick reference:
| Compound Name | Formula | Molar Mass (g/mol) |
|---|---|---|
| Water | H2O | 18.015 |
| Carbon Dioxide | CO2 | 44.009 |
| Sulfuric Acid | H2SO4 | 98.078 |
| Glucose | C6H12O6 | 180.156 |
| Sodium Chloride | NaCl | 58.443 |
| Ethanol | C2H5OH | 46.069 |
| Sodium Hydroxide | NaOH | 39.997 |
| Hydrochloric Acid | HCl | 36.461 |
Yes. The mass of an electron is negligible compared to the mass of protons and neutrons, meaning it does not meaningfully impact the molar mass at standard laboratory precision levels. You can simply type the formula of the ion (like SO4 for Sulfate) to obtain an accurate mass.
Proteins are complex chains of amino acids. If you have the exact molecular formula (e.g., Insulin is roughly C257H383N65O77S6), you can enter it directly. For large, unspecified macromolecules, chemists frequently rely on "Average Residue Mass" estimates, assuming approximately 110 Da per amino acid in the chain.
Discrepancies are usually caused by differences in rounding. Older textbooks may round Oxygen to exactly 16.00, while modern standards use the more precise 15.999. To better match typical classroom materials, try adjusting the precision dropdown to "2 decimal places".
No, the calculator will process the formula accurately regardless of element order (e.g., OH2 will yield the same result as H2O). However, using standard chemical notation (like the Hill System, which places Carbon first, then Hydrogen, then alphabetical) is recommended to prevent input mistakes.