Atomic Mass Calculator

Author: Henrick Yau

- May 14, 2025

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This calculator determines the atomic mass of specific isotopes or the molecular mass of chemical compounds.

For molecules, the total mass is the sum of all atomic masses of the constituent atoms.

Select Element:

Select Isotope:

Or enter custom isotope notation: Format: mass number followed by element symbol (e.g., 14C)

Decimal Places:

Mass Unit:

Calculation Results

Carbon

Atomic #: 6

Atomic Mass

12.0000

amu

Selected Isotope

Carbon-12

Isotope Information

Protons

Neutrons

Electrons

Natural Abundance

98.93%

H₂O

Molecular Mass

18.0153

amu

Constituent Elements

Total Atoms

Mass Breakdown by Element

Element	Symbol	Count	Atomic Mass	Total Mass	Percentage

What This Atomic Mass Calculator Does

The Atomic Mass Calculator is a tool that helps users determine the atomic mass of specific isotopes and the molecular mass of chemical compounds. It simplifies complex chemistry calculations, making it easy for students, researchers, and professionals to get accurate mass values for elements and compounds.

How Atomic Mass Is Calculated

The atomic mass of an isotope is the sum of its protons and neutrons, measured in atomic mass units (amu). For molecules, the molecular mass is the sum of the atomic masses of all the atoms in the compound.

Atomic Mass Formula:

\[ \text{Atomic Mass} = \sum (\text{Isotope Mass} \times \text{Relative Abundance}) \]

Molecular Mass Formula:

\[ \text{Molecular Mass} = \sum (\text{Atomic Mass of Each Element} \times \text{Number of Atoms}) \]

Using the Isotope and Molecular Mass Modes

This calculator has two modes: Isotope Mass Calculation and Molecular Mass Calculation. Follow these steps to use it effectively:

1. Isotope Mass Calculation

Select an element from the dropdown list.
Choose an isotope of that element.
Alternatively, enter a custom isotope notation (e.g., 13C or 235U).
Set decimal precision and select the unit (amu, g/mol, or kg/mol).
Click the "Calculate Mass" button to get the atomic mass.

2. Molecular Mass Calculation

Enter the molecular formula of a compound (e.g., H2O, C6H12O6).
Or select a common compound from the dropdown list.
Choose between natural isotopic composition or the most abundant isotope.
Click "Calculate Mass" to see the molecular weight.

Who Benefits from Atomic Mass Calculations

The Atomic Mass Calculator is useful for:

Students learning about atomic structure and molecular weight.
Chemists needing precise mass values for research.
Laboratory professionals performing chemical analysis.
Anyone working with stoichiometry and chemical equations.

Questions About Atomic Mass Calculations

What is atomic mass?

Atomic mass is the mass of an atom, measured in atomic mass units (amu). It is the total mass of an atom's protons and neutrons.

What is molecular mass?

Molecular mass is the sum of the atomic masses of all atoms in a molecule, expressed in amu or g/mol.

Supported Units for Mass Results

The calculator provides results in atomic mass units (amu), grams per mole (g/mol), and kilograms per mole (kg/mol).

What if my compound is not in the dropdown list?

You can manually enter the chemical formula using standard notation (e.g., NaCl, CH3COOH).

Accuracy and Decimal Precision

The calculator provides results with up to six decimal places. You can adjust the precision in the settings.

Reliable Atomic and Molecular Mass Tool

The Atomic Mass Calculator is a fast and reliable way to determine atomic and molecular masses. Whether for academic use, research, or chemistry applications, this tool makes calculations simple and precise.