Isotope Abundance Calculator

Mass spectrometry gives you the average atomic mass; this tool works backwards to the isotope mix that produces it. For an element with two stable isotopes, one equation pins down both percent abundances.

Isotope Abundance Calculator

$\%_1 = \frac{\bar{A} - m_2}{m_1 - m_2} \times 100$

Solve for

Average atomic mass (A_bar)

Unit

Isotopic mass 1 (m_1)

Unit

Isotopic mass 2 (m_2)

Unit

Result unit

How to interpret the result

Worked check: boron averages 10.81 u with ¹⁰B at 10.013 u and ¹¹B at 11.009 u → (10.81 − 11.009)/(10.013 − 11.009) × 100 = 19.98%, so about 20.0% ¹⁰B and 80.0% ¹¹B.

Assumptions

Two-isotope system with no other significant isotopes
Isotopic masses are the exact masses, not mass numbers