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Weighted Average Atomic Mass — result sheet
Calculate the weighted average mass of a two-isotope mixture from isotope masses and percentage abundances.
Inputs used
Results
Visual chart
Breakdown
Calculation steps
Returned data table
Formula and methodology
Formula: Average mass = mass1(abundance1/100) + mass2(abundance2/100).
An element's average atomic mass is a weighted average of its naturally occurring isotopes. This two-isotope version makes the weighting visible and requires the entered abundances to sum to 100 percent.
This result follows the calculator's declared inputs, precision, validation boundaries, and model limits.
Input contract
- Isotope 1 mass — u; minimum 1.0E-6; maximum 1000
- Isotope 1 abundance — %; minimum 0; maximum 100
- Isotope 2 mass — u; minimum 1.0E-6; maximum 1000
- Isotope 2 abundance — %; minimum 0; maximum 100
Worked example
| Input | Value |
|---|---|
| Isotope 1 mass | 12 |
| Isotope 1 abundance | 98.93 |
| Isotope 2 mass | 13 |
| Isotope 2 abundance | 1.07 |
Weighted average atomic mass is 12.0107 u.
Assumptions and limits
- Exactly two isotope abundances are represented and they sum to 100 percent.
- Masses are expressed in the same atomic-mass unit.
- The result is a mixture average, not the mass of one selected isotope.
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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