Molar mass calculator

Weights are the CIAAW 2024 standard atomic weights, abridged to five significant figures, or the older IUPAC 2005 textbook set for homework compatibility. Interval elements like chlorine use the conventional single value; the published interval is shown on the row. Elements with no standard atomic weight (technetium, promethium, and everything past bismuth except thorium, protactinium, and uranium) use the mass number of their longest-lived isotope, marked provisional in the table. Charges such as SO4^2- parse and are ignored. What this tool does not do: isotopic analysis for a specific sample, and anything needing lab-grade uncertainty figures.