Atomic Mass Calculator
Look up the atomic mass of any element from the periodic table. Enter an element symbol to see its standard atomic weight in atomic mass units (amu), along with isotope information. The atomic mass values are the foundation of all molecular weight calculations — each compound's molecular weight is built from the atomic masses of its constituent elements.
Ingrese una fórmula química arriba para calcular el peso molecular
Instant Atomic Mass Lookup
Type an element symbol to see its atomic mass instantly.
Every element has a characteristic atomic mass — the weighted average mass of its naturally occurring isotopes, expressed in atomic mass units (amu). One amu equals 1/12 the mass of a carbon-12 atom, or 1.66054 × 10⁻²⁴ grams.
For elements with a single stable isotope (like gold, ¹⁹⁷Au), the atomic mass is precisely known. For elements with multiple isotopes (like chlorine, with ³⁵Cl and ³⁷Cl), the atomic mass is a weighted average reflecting natural abundances.
Enter any element symbol — or a complete chemical formula — to see atomic masses and how they combine to form molecular weights.
Standard Atomic Weights
IUPAC 2021 standard atomic weights for selected elements.
The standard atomic weight of each element is determined by the IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW). These values are updated periodically as measurement techniques improve.
Atomic weights range from 1.008 (Hydrogen) to 294 (Oganesson). Lighter elements like H, He, C, N, O are essential for organic chemistry. Heavier elements like Fe, Cu, Ag, Au, U are important in inorganic chemistry, materials science, and nuclear physics.
Explore the element cards below to see atomic masses of elements across the periodic table.
How to Look Up Atomic Mass
Find any element's atomic mass in 3 steps.
Enter an Element Symbol
Type any element symbol (e.g., Fe for iron, Au for gold) or enter a full chemical formula to see the atomic masses of all constituent elements. The calculator recognizes all 118 elements from the IUPAC periodic table — from Hydrogen (H, Z=1) to Oganesson (Og, Z=118).
Atomic Mass Examples
Click any element to see its atomic mass and isotope information.
Atomic Mass FAQ
Questions about atomic mass, isotopes, and atomic mass units.