Average Atomic Mass Calculator
Calculate average atomic mass using isotopic masses and natural abundances for elements with multiple isotopes.
Enter Isotope Data
Isotope Data
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Results
Enter isotope data to calculate average atomic mass
Average Atomic Mass
Formula
Average Mass = Σ(Mass × Abundance) / 100
- • Weighted average of all isotopes
- • Based on natural abundance
- • Expressed in atomic mass units (amu)
- • Used in periodic table
Key Concepts
- • Isotopes have different masses
- • Natural abundance varies
- • Most elements have multiple isotopes
- • Mass number ≠ atomic mass
- • Decimal values reflect averaging
Common Elements with Multiple Isotopes
Carbon (C)
- • ¹²C: 12.000 amu, 98.9%
- • ¹³C: 13.003 amu, 1.1%
- • Average: 12.011 amu
Chlorine (Cl)
- • ³⁵Cl: 34.969 amu, 75.8%
- • ³⁷Cl: 36.966 amu, 24.2%
- • Average: 35.453 amu
Copper (Cu)
- • ⁶³Cu: 62.930 amu, 69.2%
- • ⁶⁵Cu: 64.928 amu, 30.8%
- • Average: 63.546 amu