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Molar Mass Calculator

The molar mass of a chemical formula from IUPAC standard atomic weights, with brackets and hydrates read correctly, the percentage composition by mass, and moles to grams both ways.

Built by AbhiLast reviewed September 24, 2026

Mass contributed by each element, g/molCa× 140.078 · 54.1%O× 231.998 · 43.2%H× 22.016 · 2.7%

Case matters: CO is carbon monoxide, Co is cobalt. Use brackets for groups and a dot for hydrates, as in CuSO4.5H2O.

Optional. Gives the moles in this mass of the substance.

Optional. Gives the mass of this many moles.

Result

Molar mass, g/mol74.092

IUPAC standard atomic weights for normal materials; isotopically enriched or unusual samples differ.

Percentage composition by mass
Ca 54.09%, O 43.19%, H 2.72%
Atoms of each element
Ca 1, O 2, H 2
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Results come from the published equations applied to the values you enter. They are not electrical design, conductor sizing, laboratory safety or medical guidance. Weather indices describe a standard person in standard conditions and are not a forecast. Where codes apply, local rules vary and must be checked. Read the full disclaimer

How to use the Molar Mass Calculator

  1. Type the chemical formula exactly as it is written, with capital letters where the symbols have them, such as NaCl, Ca(OH)2 or CuSO4.5H2O.
  2. Read the molar mass in grams per mole, the number of atoms of each element and each element's share of the mass.
  3. To convert, enter a mass to get the moles in it, or a number of moles to get their mass.

The formula

molar mass = sum over elements of (atoms of the element × its standard atomic weight) g/molshare of an element = its atoms × its atomic weight ÷ molar massmoles = mass in grams ÷ molar massmass in grams = moles × molar mass

Molar mass is the mass of one mole of a substance: 6.022 × 10²³ formula units. Because the atomic weights are relative to one twelfth of a carbon-12 atom, the sum of a formula’s atomic weights is also its molar mass in grams per mole.

Reading a chemical formula

The formula is read left to right. A symbol is a capital letter, with one lower-case letter if the element’s symbol has one, so Cl is chlorine and CCl4 is one carbon and four chlorine. A number after a symbol counts its atoms. A number after a closing bracket multiplies every atom inside the bracket.

That last rule is where formulas are most often misread. In Ca(OH)2 the 2 applies to the whole hydroxide group:

Reading it as CaOH2, with the 2 on the hydrogen only, drops an oxygen and gives a plausible-looking number that is wrong. Brackets nest to any depth, and square brackets work the same way as round ones.

Hydrates and the dot

A dot joins the parts of an addition compound. In a hydrate the second part is water, and a number straight after the dot multiplies that whole part: CuSO4·5H2O counts 5 × H2O, which is 10 hydrogen and 5 oxygen, on top of the 4 oxygen in the sulfate. The page accepts a full stop, a middle dot (·), a bullet or an asterisk for the dot.

Case matters

Symbols are case-sensitive. CO is carbon monoxide, one carbon and one oxygen; Co is cobalt, one element. Writing co in lower case is refused, and the page names the part it could not read, rather than choosing one reading for you. An unknown symbol such as Xx is refused by name too.

Percentage composition

Each element’s share of the molar mass is its atoms times its atomic weight, divided by the molar mass. The shares add up to 100%, give or take the last displayed decimal place, since each is rounded separately.

The atomic weights

The atomic weights are the IUPAC standard atomic weights published by its Commission on Isotopic Abundances and Atomic Weights (CIAAW). Fourteen elements, including hydrogen, carbon, nitrogen, oxygen, sulfur and chlorine, vary enough in nature that IUPAC publishes their atomic weight as an interval. For those the page uses the single conventional value CIAAW gives for everyday use, such as 12.011 for carbon.

Every element that has a standard atomic weight is included. Elements with no stable isotope, such as technetium, radon and plutonium, have none: their molar mass depends on which isotope is meant, so the page refuses them rather than invent a value. Isotopically enriched materials, and charges on ions, are outside what this page does.

With your numbers

  1. Ca: 1 × 40.078 = 40.078 g/mol (54.09%)
  2. O: 2 × 15.999 = 31.998 g/mol (43.19%)
  3. H: 2 × 1.008 = 2.016 g/mol (2.72%)
  4. Molar mass = 74.092 g/mol
  5. Moles = 10 g ÷ 74.092 g/mol = 0.134967 mol
  6. Mass = 0.5 mol × 74.092 g/mol = 37.046 g

Quick reference

IUPAC standard atomic weights for normal materials; isotopically enriched or unusual samples differ.

Worked examples from the published equations, for United States.
ExampleMolar mass, g/mol
Water, H2O18.015
Salt, NaCl58.4398
Calcium hydroxide, Ca(OH)274.092
Glucose, C6H12O6180.156
Aluminium sulfate, Al2(SO4)3342.1311
Copper sulfate pentahydrate249.677
Carbon monoxide, CO28.01
Cobalt, Co58.9332

Where the numbers come from

The fixed figures this calculator relies on, and the published source each one was checked against. How the calculators are built and checked

15 sources

  1. CIAAW, Abridged Standard Atomic Weights 2024 (https://www.ciaaw.org/abridged-atomic-weights.htm): the abridged value that replaces the conventional atomic weight for an interval element, per Prohaska et al., Pure Appl. Chem. 94(5) 573-600 (2022), Table 1 column 7. The standard atomic weight is the interval [1.00784, 1.00811].

    Used for

    • Conventional atomic weight of hydrogen; IUPAC publishes the interval [1.00784, 1.00811].

  2. CIAAW, Standard Atomic Weights 2024 (https://www.ciaaw.org/atomic-weights.htm), the table of Prohaska et al., "Standard atomic weights of the elements 2021 (IUPAC Technical Report)", Pure Appl. Chem. 94(5) 573-600 (2022), Table 1, with the 2024 revisions of Gd, Lu and Zr.

    Used for

    • Standard atomic weight of helium.
    • Standard atomic weight of beryllium.
    • Standard atomic weight of fluorine.
    • Standard atomic weight of neon.
    • Standard atomic weight of sodium.
    • Standard atomic weight of aluminium.
    • Standard atomic weight of phosphorus.
    • Standard atomic weight of potassium.
    • Standard atomic weight of calcium.
    • Standard atomic weight of scandium.
    • Standard atomic weight of titanium.
    • Standard atomic weight of vanadium.
    • Standard atomic weight of chromium.
    • Standard atomic weight of manganese.
    • Standard atomic weight of iron.
    • Standard atomic weight of cobalt.
    • Standard atomic weight of nickel.
    • Standard atomic weight of copper.
    • Standard atomic weight of zinc.
    • Standard atomic weight of gallium.
    • Standard atomic weight of germanium.
    • Standard atomic weight of arsenic.
    • Standard atomic weight of selenium.
    • Standard atomic weight of krypton.
    • Standard atomic weight of rubidium.
    • Standard atomic weight of strontium.
    • Standard atomic weight of yttrium.
    • Standard atomic weight of zirconium.
    • Standard atomic weight of niobium.
    • Standard atomic weight of molybdenum.
    • Standard atomic weight of ruthenium.
    • Standard atomic weight of rhodium.
    • Standard atomic weight of palladium.
    • Standard atomic weight of silver.
    • Standard atomic weight of cadmium.
    • Standard atomic weight of indium.
    • Standard atomic weight of tin.
    • Standard atomic weight of antimony.
    • Standard atomic weight of tellurium.
    • Standard atomic weight of iodine.
    • Standard atomic weight of xenon.
    • Standard atomic weight of caesium.
    • Standard atomic weight of barium.
    • Standard atomic weight of lanthanum.
    • Standard atomic weight of cerium.
    • Standard atomic weight of praseodymium.
    • Standard atomic weight of neodymium.
    • Standard atomic weight of samarium.
    • Standard atomic weight of europium.
    • Standard atomic weight of gadolinium.
    • Standard atomic weight of terbium.
    • Standard atomic weight of dysprosium.
    • Standard atomic weight of holmium.
    • Standard atomic weight of erbium.
    • Standard atomic weight of thulium.
    • Standard atomic weight of ytterbium.
    • Standard atomic weight of lutetium.
    • Standard atomic weight of hafnium.
    • Standard atomic weight of tantalum.
    • Standard atomic weight of tungsten.
    • Standard atomic weight of rhenium.
    • Standard atomic weight of osmium.
    • Standard atomic weight of iridium.
    • Standard atomic weight of platinum.
    • Standard atomic weight of gold.
    • Standard atomic weight of mercury.
    • Standard atomic weight of bismuth.
    • Standard atomic weight of thorium.
    • Standard atomic weight of protactinium.
    • Standard atomic weight of uranium.

  3. CIAAW, Abridged Standard Atomic Weights 2024 (https://www.ciaaw.org/abridged-atomic-weights.htm): the abridged value that replaces the conventional atomic weight for an interval element, per Prohaska et al., Pure Appl. Chem. 94(5) 573-600 (2022), Table 1 column 7. The standard atomic weight is the interval [6.938, 6.997].

    Used for

    • Conventional atomic weight of lithium; IUPAC publishes the interval [6.938, 6.997].

  4. CIAAW, Abridged Standard Atomic Weights 2024 (https://www.ciaaw.org/abridged-atomic-weights.htm): the abridged value that replaces the conventional atomic weight for an interval element, per Prohaska et al., Pure Appl. Chem. 94(5) 573-600 (2022), Table 1 column 7. The standard atomic weight is the interval [10.806, 10.821].

    Used for

    • Conventional atomic weight of boron; IUPAC publishes the interval [10.806, 10.821].

  5. CIAAW, Abridged Standard Atomic Weights 2024 (https://www.ciaaw.org/abridged-atomic-weights.htm): the abridged value that replaces the conventional atomic weight for an interval element, per Prohaska et al., Pure Appl. Chem. 94(5) 573-600 (2022), Table 1 column 7. The standard atomic weight is the interval [12.0096, 12.0116].

    Used for

    • Conventional atomic weight of carbon; IUPAC publishes the interval [12.0096, 12.0116].

  6. CIAAW, Abridged Standard Atomic Weights 2024 (https://www.ciaaw.org/abridged-atomic-weights.htm): the abridged value that replaces the conventional atomic weight for an interval element, per Prohaska et al., Pure Appl. Chem. 94(5) 573-600 (2022), Table 1 column 7. The standard atomic weight is the interval [14.00643, 14.00728].

    Used for

    • Conventional atomic weight of nitrogen; IUPAC publishes the interval [14.00643, 14.00728].

  7. CIAAW, Abridged Standard Atomic Weights 2024 (https://www.ciaaw.org/abridged-atomic-weights.htm): the abridged value that replaces the conventional atomic weight for an interval element, per Prohaska et al., Pure Appl. Chem. 94(5) 573-600 (2022), Table 1 column 7. The standard atomic weight is the interval [15.99903, 15.99977].

    Used for

    • Conventional atomic weight of oxygen; IUPAC publishes the interval [15.99903, 15.99977].

  8. CIAAW, Abridged Standard Atomic Weights 2024 (https://www.ciaaw.org/abridged-atomic-weights.htm): the abridged value that replaces the conventional atomic weight for an interval element, per Prohaska et al., Pure Appl. Chem. 94(5) 573-600 (2022), Table 1 column 7. The standard atomic weight is the interval [24.304, 24.307].

    Used for

    • Conventional atomic weight of magnesium; IUPAC publishes the interval [24.304, 24.307].

  9. CIAAW, Abridged Standard Atomic Weights 2024 (https://www.ciaaw.org/abridged-atomic-weights.htm): the abridged value that replaces the conventional atomic weight for an interval element, per Prohaska et al., Pure Appl. Chem. 94(5) 573-600 (2022), Table 1 column 7. The standard atomic weight is the interval [28.084, 28.086].

    Used for

    • Conventional atomic weight of silicon; IUPAC publishes the interval [28.084, 28.086].

  10. CIAAW, Abridged Standard Atomic Weights 2024 (https://www.ciaaw.org/abridged-atomic-weights.htm): the abridged value that replaces the conventional atomic weight for an interval element, per Prohaska et al., Pure Appl. Chem. 94(5) 573-600 (2022), Table 1 column 7. The standard atomic weight is the interval [32.059, 32.076].

    Used for

    • Conventional atomic weight of sulfur; IUPAC publishes the interval [32.059, 32.076].

  11. CIAAW, Abridged Standard Atomic Weights 2024 (https://www.ciaaw.org/abridged-atomic-weights.htm): the abridged value that replaces the conventional atomic weight for an interval element, per Prohaska et al., Pure Appl. Chem. 94(5) 573-600 (2022), Table 1 column 7. The standard atomic weight is the interval [35.446, 35.457].

    Used for

    • Conventional atomic weight of chlorine; IUPAC publishes the interval [35.446, 35.457].

  12. CIAAW, Abridged Standard Atomic Weights 2024 (https://www.ciaaw.org/abridged-atomic-weights.htm): the abridged value that replaces the conventional atomic weight for an interval element, per Prohaska et al., Pure Appl. Chem. 94(5) 573-600 (2022), Table 1 column 7. The standard atomic weight is the interval [39.792, 39.963].

    Used for

    • Conventional atomic weight of argon; IUPAC publishes the interval [39.792, 39.963].

  13. CIAAW, Abridged Standard Atomic Weights 2024 (https://www.ciaaw.org/abridged-atomic-weights.htm): the abridged value that replaces the conventional atomic weight for an interval element, per Prohaska et al., Pure Appl. Chem. 94(5) 573-600 (2022), Table 1 column 7. The standard atomic weight is the interval [79.901, 79.907].

    Used for

    • Conventional atomic weight of bromine; IUPAC publishes the interval [79.901, 79.907].

  14. CIAAW, Abridged Standard Atomic Weights 2024 (https://www.ciaaw.org/abridged-atomic-weights.htm): the abridged value that replaces the conventional atomic weight for an interval element, per Prohaska et al., Pure Appl. Chem. 94(5) 573-600 (2022), Table 1 column 7. The standard atomic weight is the interval [204.382, 204.385].

    Used for

    • Conventional atomic weight of thallium; IUPAC publishes the interval [204.382, 204.385].

  15. CIAAW, Abridged Standard Atomic Weights 2024 (https://www.ciaaw.org/abridged-atomic-weights.htm): the abridged value that replaces the conventional atomic weight for an interval element, per Prohaska et al., Pure Appl. Chem. 94(5) 573-600 (2022), Table 1 column 7. The standard atomic weight is the interval [206.14, 207.94].

    Used for

    • Conventional atomic weight of lead; IUPAC publishes the interval [206.14, 207.94].

Common questions about the Molar Mass Calculator

How do I read a chemical formula?
Each element symbol is one capital letter, sometimes followed by one lower-case letter. The number after a symbol is how many atoms of it there are, and no number means one. A number after a bracket multiplies everything inside the bracket, so Ca(OH)2 has one calcium, two oxygen and two hydrogen atoms. Brackets can sit inside brackets, as in K4[Fe(CN)6].
What does the dot mean in a hydrate?
It joins two parts of one formula unit, most often a salt and the water held in its crystals. CuSO4·5H2O is copper sulfate with five water molecules per formula unit, and the 5 multiplies the whole H2O. Its molar mass includes that water, which is why the blue crystals weigh more per mole than the white anhydrous powder. Type the dot as a full stop, a middle dot or an asterisk.
Why is CO different from Co?
CO is two symbols, carbon then oxygen: carbon monoxide. Co is one symbol, cobalt. The calculator reads case exactly as typed and does not guess, so co in lower case is refused rather than read as either.
What is the difference between molar mass and molecular weight?
Molecular weight, properly relative molecular mass, is the same sum of atomic weights with no unit. Molar mass is the mass of one mole, in grams per mole, and has the same number. For salts and metals, which are not made of molecules, formula mass or molar mass is the more accurate name.
Why do other tables give slightly different values?
Atomic weights are revised as measurements improve, and older tables used values such as 1.00794 for hydrogen. This page uses the current IUPAC standard atomic weights, so a result can differ from an old textbook in the second or third decimal place.

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