Use this element weights lookup to find atomic weight by symbol, name, or atomic number, then convert grams to moles, atoms, or target grams for one element.
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Look up atomic weight, moles, atoms, and target grams Search by symbol, full name, or atomic number to retrieve the standard atomic weight. If you also
enter a sample mass or target mole amount, the worksheet converts between grams, moles, and an approximate atom count.
Example lookups
Enter an element to begin Use a symbol like Fe, a name like Iron, or an atomic number like 26 to load the lookup result.
Element weights lookup guide: atomic weights, grams-to-moles conversion, and atom counts
An element-weight lookup is most useful when it does more than display a number from the periodic table. This page lets you search an element by symbol, name, or atomic number, then use the listed atomic weight to convert a gram amount into moles and an approximate atom count.
What an element-weight lookup should tell you
Atomic weight is the periodic-table value used for routine element mass calculations. For a lookup tool to be practical, it should not stop at the element name and symbol. It should also tell you the atomic number, broad chemical family, and the standard atomic-weight value you would actually use in introductory chemistry work.
That is why this page treats lookup as the start of a calculation workflow. Once an element is identified, the same result can support grams-to-moles conversion and an approximate atom count without sending you to a second tool.
How the gram-to-mole conversion works
The listed atomic weight is used as the molar mass for the elemental substance in grams per mole. Once you know that value, converting a measured mass into amount of substance is a direct division: grams divided by atomic weight gives moles.
If you also want an atom count, multiply the mole amount by Avogadro's number. This is the same counting relationship used throughout chemistry: one mole corresponds to 6.022 × 10²³ atoms, molecules, or formula units depending on the substance under discussion.
moles = mass (g) / atomic weight (g/mol)
Converts the entered gram amount into amount of substance for the selected element.
atoms = moles × 6.022 × 10²³
Uses Avogadro's number to estimate how many atoms are present in that sample.
Worked example: iron
Suppose you look up iron and enter 55.84 g. The page shows an atomic weight of 55.84 g/mol, so the sample corresponds to 1 mole of iron atoms.
That same result means the sample contains approximately 6.022 × 10²³ iron atoms. If you instead entered 27.92 g, the mole amount would be about 0.5 mol and the atom count would be about half of Avogadro's number.
Planning a target mole amount from an element's atomic weight
Search results for atomic weights often stop at a periodic-table row. The calculator on this page adds the reverse planning step: choose an element, enter the target amount in moles, and read the gram mass that corresponds to that element's atomic weight.
That target-mole view is useful when a class worksheet or lab note says to prepare a set amount of elemental iron, carbon, sodium, or another pure element. Multiplying the desired moles by the atomic weight gives the grams to weigh before you move to a separate stoichiometry or solution-preparation calculation.
grams = target moles × atomic weight (g/mol)
Converts a target amount of a selected element into the gram mass needed for that amount of substance.
Atomic weight, atomic mass, and periodic-table lookup wording
People search for the same idea with several phrases: element weight, atomic weight, atomic mass, molar mass of an element, and periodic-table atomic mass. For ordinary element lookup work, the value shown here is the standard atomic-weight reference value used numerically as grams per mole.
That does not mean every atom of the element has exactly that mass. Many elements occur as a natural mixture of isotopes, so the standard atomic weight is an average reference value for normal materials. Isotope-specific questions need an isotope table or mass-spectrometry reference rather than a general element-weight lookup.
When to use a related chemistry calculator
Use this page when the substance is a single element and you need atomic number, symbol, standard atomic weight, grams-to-moles conversion, target grams, or an approximate atom count. The input should be one element, not a whole formula.
If the task involves H2O, NaCl, Ca(OH)2, hydrates, or any formula with more than one element, a molecular-weight calculator is the right workflow because it has to count each element in the formula before summing the molar mass. If the molar mass is already known and you only need a unit conversion, a grams-to-moles or moles-to-grams converter may be faster.
This page uses standard atomic-weight values for elemental lookups. It does not replace isotope-specific mass tables, mass-spectrometry data, or full compound stoichiometry tools.
Use it for periodic-table reference, classroom conversions, and quick elemental mass work. For molecular formulas, isotopic composition, or reaction stoichiometry, use a dedicated chemistry calculator built for those tasks.
Further reading
PubChem periodic table — NIH-hosted periodic table reference covering atomic numbers, masses, and broad element properties.
NIST Chemistry WebBook — NIST chemistry reference used for deeper property and substance lookups beyond the periodic-table summary level.
Frequently asked questions
Is atomic weight the same as molar mass for an element?
For routine chemistry calculations, yes. The atomic-weight value from the periodic table is used numerically as the molar mass in grams per mole for the elemental substance.
Why is the atom count only approximate?
Because standard atomic weights are average values that reflect natural isotopic abundance. The counting conversion is still the correct chemistry relationship, but the displayed atom total is an estimate based on the listed average mass value.
How do I find the atomic weight of an element quickly?
Enter the element symbol, element name, or atomic number. For example, Fe, Iron, and 26 all load iron, including its atomic number, standard atomic weight, broad group or block, and ordinary reference state.
Can I calculate grams from a target number of moles?
Yes. Enter the element and the target amount in moles. The calculator multiplies the target moles by the element's atomic weight in g/mol to show the gram mass to weigh for that target amount.
Can I use this page for compounds like H2O or NaCl?
No. This lookup is for individual elements only. For compounds, use a molar-mass or chemical-compound calculator that adds the atomic contributions from every element in the formula.
Why do atomic weights use decimals?
Most naturally occurring elements are mixtures of isotopes. A decimal atomic weight represents the weighted average used for normal chemistry calculations rather than the exact mass of one single isotope.
What is the difference between atomic number and atomic weight?
Atomic number counts protons and identifies the element. Atomic weight is a mass reference value used in mole and gram calculations. Iron has atomic number 26, while its standard atomic weight is about 55.84 g/mol.
Should I use this for isotope-specific mass calculations?
No. Use an isotope or nuclide reference when the problem names a specific isotope, monoisotopic mass, radioactive nuclide, or mass-spectrometry method. This page is for standard elemental reference values.
Why do some heavy elements have expected states rather than ordinary labels?
For some superheavy elements, the standard state at ordinary conditions is predicted from theory rather than established from macroscopic bulk samples. The lookup preserves that reference wording instead of overstating certainty.
