Average Atomic Mass Calculator
Calculate an element's average atomic mass as the weighted average of its isotope masses by natural abundance.
Average Atomic Mass Mathematics
Average atomic mass calculator computes an element's weighted average atomic mass from its isotope masses and natural abundances.
The atomic mass shown on the periodic table is a weighted average across all naturally occurring isotopes of an element, weighted by how abundant each isotope actually is in nature.
- 1Enter each isotope's mass (amu) and natural abundance (%).
- 2Add or remove isotopes as needed β abundances should sum to 100%.
- 3View the weighted average atomic mass.
Chlorine has two natural isotopes: Cl-35 (mass 34.969, abundance 75.77%) and Cl-37 (mass 36.966, abundance 24.23%).
Frequently Asked Questions (FAQ)
Individual isotopes have nearly whole-number masses, but the periodic table value averages multiple isotopes weighted by their natural abundance, producing a decimal value that reflects the real isotope mixture found in nature.
With a single isotope at 100% abundance, the average atomic mass simply equals that isotope's mass β the weighted average formula still applies, just with only one term.
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