Atomic and molecular mass Calculator
Calculation Method
Element List
| Element | Symbol | Atomic Mass (u) | Atoms | Subtotal (u) | Action |
|---|---|---|---|---|---|
| No elements added yet. | |||||
| Molecular Mass: | — u | ||||
Custom Element List
| Element | Symbol | Atomic Mass (u) | Atoms | Subtotal (u) | Action |
|---|---|---|---|---|---|
| No custom elements added yet. | |||||
| Molecular Mass: | — u | ||||
Step-by-Step Calculation
Select an element, set the atom count, then click Calculate Molecular Mass to see the analysis.
Complete Guide to Atomic Mass & Molecular Mass
Introduction
The atomic mass (also called atomic weight) is the average mass of an atom of an element, measured in unified atomic mass units (u) or daltons (Da). It is a fundamental property in chemistry, underpinning stoichiometry, molar calculations, and the quantitative analysis of chemical reactions. The molecular mass (or molecular weight) is the sum of the atomic masses of all atoms in a molecule, and is critical for determining molar concentrations, preparing solutions, and understanding reaction yields.
This calculator provides three convenient ways to compute molecular mass: selecting elements from a periodic table list, entering a chemical formula directly, or defining custom elements with user-specified atomic masses.
What is Atomic Mass?
Atomic mass is the mass of a single atom of a chemical element. It is expressed in unified atomic mass units (u), where 1 u is defined as one-twelfth of the mass of a carbon-12 atom. In practical chemistry, atomic mass is commonly expressed in grams per mole (g/mol), which is numerically equivalent to the atomic mass in u.
- Isotopic abundance: The atomic mass listed on the periodic table is a weighted average of the masses of all naturally occurring isotopes of that element.
- Standard atomic weights: These values are determined by IUPAC and updated periodically.
- Units: Atomic mass is measured in u. For example, carbon has an atomic mass of 12.011 u.
What is Molecular Mass?
Molecular mass is the sum of the atomic masses of all atoms in a molecule: Molecular Mass (in u) = Σ (Atomic Mass × Number of Atoms).
- For H₂O: (2 × 1.008) + (1 × 15.999) = 18.015 u
- For CO₂: (1 × 12.011) + (2 × 15.999) = 44.009 u
- For C₆H₁₂O₆: (6 × 12.011) + (12 × 1.008) + (6 × 15.999) = 180.156 u
Note: The molecular mass in u is numerically equal to the molar mass in g/mol. This relationship is the foundation of all stoichiometric calculations.
How to Use the Atomic Mass Calculator
- Elements Selector: Pick an element, set the atom count, then click "Calculate Molecular Mass" to add it and see results. Use "Add Element" to manually build multi‑element compounds.
- Formula Input: Type a formula like H2O or Ca(OH)2, then click "Calculate Molecular Mass".
- Custom Elements: Define your own elements with custom atomic masses for isotopes or novel compounds.
Common Molecular Masses
| Compound | Formula | Molecular Mass (u) |
|---|---|---|
| Water | H₂O | 18.015 |
| Carbon Dioxide | CO₂ | 44.009 |
| Glucose | C₆H₁₂O₆ | 180.156 |
| Sodium Chloride | NaCl | 58.443 |
| Sulfuric Acid | H₂SO₄ | 98.079 |