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Isotopic Average Atomic Mass Calculator

Weighted average mass from isotope abundances.

Compute the average atomic mass of an element from up to four isotopes' masses and natural abundances: M_avg = Σ (abundance_i · mass_i) / Σ abundance_i.

Dr. Helena Ortiz By Dr. Helena Ortiz
Published Last reviewed 1 min read

Inputs

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Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

M_avg = Σ aᵢ · mᵢ / Σ aᵢ

In depth

Compute the average atomic mass of an element from up to four isotopes' masses and natural abundances: M_avg = Σ (abundance_i · mass_i) / Σ abundance_i.