How to use the average atomic mass calculator
Compute atomic mass from isotope abundances. Enter isotope 1 mass, isotope 1 abundance, isotope 2 mass in the fields above; the isotope 2 abundance, average atomic mass are computed instantly and plotted on the chart so you can see how the answer changes.
Formula
Variables
- m1 — Isotope 1 mass (u)
- p1 — Isotope 1 abundance (%)
- m2 — Isotope 2 mass (u)
Worked example
With isotope 1 mass = 34.969 u, isotope 1 abundance = 75.76 %, isotope 2 mass = 36.966 u, the calculator gives isotope 2 abundance ≈ 24.24 %; average atomic mass ≈ 35.45307 u.
Frequently asked questions
What is the formula for the average atomic mass calculation?
Isotope 2 abundance (%) = 100-p1. Average atomic mass (u) = (m1 × p1+m2 × [Isotope 2 abundance]) / 100. Here m1 is isotope 1 mass (u), p1 is isotope 1 abundance (%), m2 is isotope 2 mass (u).
What inputs do I need for the average atomic mass calculator?
You need isotope 1 mass in u, isotope 1 abundance in %, isotope 2 mass in u. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use this calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.