Atomic Mass Calculator

Calculate the weighted average atomic mass from isotope lists with precision and clarity using a clean white layout Add or remove rows set masses and abundances see charted contributions validate totals and export data as CSV or PDF with one click for labs classrooms and research Includes example chlorine isotopes dataset to start quickly

Isotope Inputs

	Isotope	Isotopic Mass (u)	Abundance (%)	Contribution (u)

Tip: Use exact masses in unified atomic mass units (u). Abundances may be entered as percentages; they will be internally converted to fractions.

Results

0.000000

Abundance sum: 0.00%

Calculation steps

Graph

Bars show each isotope's contribution m_i × a_i/100 in u.

Formula Used

Weighted average atomic mass:

M = Σ_i ( a_i/100 × m_i )

m_i = isotopic mass in unified atomic mass units (u).
a_i = natural abundance in percent for isotope i.

1 u ≈ 1.660 539 066 60 × 10⁻²⁷ kg (atomic mass constant).

Example Data

Natural chlorine isotopes:

Isotope	Mass (u)	Abundance (%)
Cl-35	34.968852682	75.78
Cl-37	36.965902602	24.22

Expected atomic mass ≈ 35.453 u.