What it does
ChemCalc calculates molecular weight, monoisotopic mass, elemental composition and isotope distributions from chemical formulas.
ChemCalc separates molecular weight, monoisotopic mass, elemental composition and isotope distributions, with notation for groups, charges, salts and specified isotopes. Its formula finder returns candidates for a measured mass rather than identifying a compound uniquely. The REST documentation makes the search assumptions explicit: allowed element/group ranges, precision in ppm, possible ionizations, neutral-molecule inclusion and a result limit. Documented API defaults include 100 ppm and 1,000 results; these are API defaults, not a claim about every browser form. Isotope-distribution output can be XY data with optional Gaussian broadening. Choose the mass quantity, charge/adduct assumptions and allowed elements before interpreting a candidate list.
Strengths
- Multiple mass and isotope-distribution calculations
- Supports groups, charges and isotope-specific notation
Best for
- Checking a molecular formula for mass-spectrometry work
Sources
- Mass spectrometry molecular formula calculator | ChemCalc (Oct 26, 2026)
- ChemCalc REST Formula Search and Isotope Distribution Parameters (Oct 26, 2026)