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Isotope-Weighted Atomic Mass — result sheet
Calculate an element's average atomic mass from isotope masses and their percentage abundances.
Inputs used
Results
Visual chart
Breakdown
Calculation steps
Returned data table
Formula and methodology
Formula: Average atomic mass = Σ(isotope mass × fractional abundance), with fractional abundance = percentage / 100.
The periodic-table atomic mass is a weighted average rather than the mass of one isotope. Each isotope contributes in proportion to its abundance, so the abundance list must describe the same isotope order as the mass list and total 100%.
This result follows the calculator's declared inputs, precision, validation boundaries, and model limits.
Input contract
- Isotope masses — Comma-separated atomic-mass values.
- Abundances — Comma-separated percentages in the same order; they must total 100%.
Worked example
| Input | Value |
|---|---|
| Isotope masses | 12, 13.0034 |
| Abundances | 98.93, 1.07 |
12.0107 u
Assumptions and limits
- Masses and abundances refer to isotopes of one element and are listed in matching order.
- Abundances are percentage values that total 100% within a small rounding tolerance.
- The result is an average atomic mass in unified atomic mass units and does not identify an isotope distribution automatically.
Calculator note
Source and methodology
Use the official WorldCalculate methodology policy for the source, formula, precision, and boundary standards behind this calculator.
Planning estimate, not financial, medical, legal, or professional advice. © WorldCalculate — reuse with attribution. Built and curated by Hassan ALRowaie.
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