Molar mass · IUPAC

Molar mass calculator with IUPAC atomic weights

Get the hydrate molar mass right before anyone weighs a gram.

Type a formula with brackets or hydrate water and get the molar mass, element percentages and grams to moles.

Last updated 2026-09-27. Math runs in your browser, no data leaves your computer.

Type the formula exactly as it appears on the certificate of analysis, including any water of crystallisation. The tool reads round and square brackets, and it treats a middle dot, an asterisk or a full stop as the hydrate separator.

Symbols are case sensitive, so Co is cobalt while CO is carbon and oxygen, and a wrong capital changes the answer by a wide margin.

Grams return mol, kilograms return kmol, and pounds return lb-mol for plant mass balances, so the unit you pick sets the unit you get back.

Moles here follow the mass unit on the left, so mol gives grams, kmol gives kilograms and lb-mol gives pounds to weigh.

Before the booking, screen the name on the invoice. Shipment pre-check is on the paid plans, from USD 59 a month.

General guidance only. Verify against the cited primary sources before you commit to a shipment, declaration, or contract.

How the molar mass is built

The most common costly error is weighing a hydrate against the anhydrous molar mass, or the other way round. Copper sulfate pentahydrate carries five waters worth 90 g/mol, so a recipe written for the anhydrous salt and filled with the pentahydrate delivers only about 64% of the copper it promised, and nobody notices until the plating bath or the feed premix fails its assay.

The parser reads the formula left to right, multiplies each bracketed group by the number after it, and adds any hydrate part multiplied by its leading number. Each element count is then multiplied by its standard atomic weight from the IUPAC abridged table 2024, and the products are summed. Mass percent per element is its share of that sum.

Grams to moles is mass divided by molar mass. Because g/mol, kg/kmol and lb/lb-mol are the same number, the tool keeps the unit you entered and scales the mole unit to match, and pounds convert to grams at exactly 453.59237 g per pound as defined in NIST Special Publication 811.

Worked example: copper sulfate for a 0.1 M bath

The booking. A process sheet calls for 0.1 mol of copper sulfate per liter and quotes the molar mass as 159.60 g/mol, so the operator weighs 15.96 g per liter into the tank. The bag on the pallet is labelled copper sulfate, the scale reads true, and on paper the bath is at strength.

The failure. The bag holds the pentahydrate, CuSO4·5H2O, which weighs 249.677 g/mol, so 15.96 g is only 15.96 / 249.677 = 0.0639 mol. The bath runs 36% short of copper, and the options are to top up and re-assay the whole tank or to scrap the run.

The fix. Type the formula from the certificate of analysis, including the five waters, and the tool returns 249.677 g/mol. Weighing 0.1 x 249.677 = 24.97 g per liter puts the bath on 0.1 M, and the assay passes the first time.

Ready to turn the molar mass into a solution strength or to convert a percent stock acid into moles per liter? The molarity calculator takes this number and also plans the dilution volume.

Comparing two supplier quotes where one sells the hydrate and one sells the anhydrous grade? The assay and moisture price calculator puts both on a 100% active basis so the cheaper offer is the real one.

Frequently asked

Where do the atomic weights come from?

Every value comes from the IUPAC abridged standard atomic weights 2024, published by the Commission on Isotopic Abundances and Atomic Weights. Those values are quoted to five significant figures where natural isotope variation allows, which is why lithium reads 6.94 and chlorine reads 35.45 with fewer decimals than most other elements.

How do I enter a hydrate like copper sulfate pentahydrate?

Type the dot as a middle dot, an asterisk or a full stop, so CuSO4·5H2O, CuSO4*5H2O and CuSO4.5H2O all return 249.677 g/mol. The number after the dot multiplies the whole water group. For a fractional hydrate such as CaSO4·0.5H2O, use the middle dot or the asterisk so the decimal point is read as part of the number.

Why does the calculator reject technetium or radium?

Those elements have no stable isotopes, so IUPAC publishes no standard atomic weight for them and the molar mass depends on which isotope you hold. The tool stops instead of guessing, and you should take the mass number from the isotope certificate that ships with the material.

How do I convert grams to moles?

Divide the mass in grams by the molar mass in g/mol. For 100 g of sodium chloride at 58.440 g/mol that is 1.711 mol. The tool also takes pounds and returns pound moles, which is the unit most plant mass balances kept in pounds use.

Need a factory for this chemical?

Tell us the chemical, grade and quantity. A person on our team in Shanghai sends you a real, checked factory, and your first one is free.

Get your free Factory Match Or talk to our team

Related tools

Sourzi shows what official files say. It is not customs or legal advice. For a binding answer, ask a licensed customs broker, a CBP ruling or an Australian Border Force Tariff Advice.

File dates and links are on Data sources.