Formula
average mass=Σ(mass × fractional abundance).
- Use the units shown beside each field.
- Results update automatically whenever you change an input.
- Displayed values use up to four decimal places, or scientific notation for very small or large numbers. Calculations use standard floating-point arithmetic; exact integer and fraction tools identify their own precision rules.
- Enter isotope masses rather than integer mass numbers when measured precision is required.
Example Calculation
Example inputs
- Isotope masses (u): 10,11
- Abundances (%): 20,80
Masses 10 u and 11 u with abundances 20% and 80% average to 10.8 u.
Frequently asked questions
How do I use this calculator?
Enter isotope masses (u), abundances (%). The result updates automatically. Use Reset to restore the example values.
What method does it use?
average mass=Σ(mass × fractional abundance).. Enter isotope masses rather than integer mass numbers when measured precision is required.
Why might a rounded result differ?
The calculation keeps full numeric precision internally, then rounds the displayed result. Rounding intermediate steps by hand can produce a slightly different answer.
Are my inputs saved online?
No. This calculator processes your inputs in your browser. A recently used list stores only calculator names on this device, not your entered values.
Check the assumptions and units before using this result. Read about calculation methods.