Calculate molar mass
Enter a case-sensitive chemical formula with standard element symbols.
About molar mass
Molar mass is the mass of one mole of a substance, expressed in grams per mole. A mole contains a fixed number of representative particles, so molar mass connects the microscopic composition shown by a chemical formula with a mass that can be measured in a laboratory. For an element, the molar mass is numerically equal to its standard atomic mass. For a compound, it is the sum of the atomic masses of every atom represented in the formula.
The calculator reads element symbols as a capital letter followed, when appropriate, by a lowercase letter. It then applies each positive integer subscript to the preceding element. In H2O, two hydrogen atoms contribute 2.016 grams per mole and one oxygen atom contributes 15.999 grams per mole, producing 18.015 grams per mole. Capitalization matters: Co denotes cobalt, while CO represents one carbon atom and one oxygen atom.
Parentheses allow a repeated group of atoms to be represented compactly. In Ca(OH)2, the multiplier two applies to both oxygen and hydrogen inside the group. The calculation therefore adds one calcium, two oxygen, and two hydrogen contributions for a total of 74.092 grams per mole. Nested parenthesized groups are also interpreted systematically. A missing closing parenthesis, an unknown symbol, an unsupported separator, or a zero subscript is treated as an invalid formula rather than silently guessed.
Molar mass is central to stoichiometry, solution preparation, gas calculations, and analytical chemistry. Dividing a sample mass by molar mass gives the amount in moles; multiplying moles by molar mass returns mass. Atomic weights are conventional averaged values, so published tables can differ slightly in their final decimal places. This calculator uses consistent common standard values and rounds only the displayed total to six decimal places. It is designed for ordinary neutral formulas made from supported elements. Hydrate dots, isotope notation, charges, reaction arrows, and coefficients belong to broader chemical notation and should not be included in the formula field.
When recording a calculation, keep the original formula beside the result and state the atomic-weight convention if exceptional precision matters. A correctly calculated molar mass does not by itself confirm a sample's identity or purity, but it provides the conversion factor needed to connect balances, volumetric measurements, and balanced equations.
Molar mass FAQ
Are molar mass and molecular weight the same?
They are often used interchangeably in routine work, but molar mass has units of grams per mole. Relative molecular mass is formally a dimensionless ratio.
Why is capitalization important in a formula?
Element symbols always begin with a capital letter and may have one lowercase letter. Changing capitalization can identify a different element or make the formula invalid.
How are parentheses calculated?
The mass of every element inside a parenthesized group is added first. That group total is then multiplied by the integer immediately after the closing parenthesis.
Why might another periodic table give a slightly different result?
Standard atomic weights may be updated or rounded to different precision by different references. Small last-decimal differences generally reflect those conventions rather than a calculation error.
Can I enter a reaction or ionic charge?
No, the input is intended for one neutral chemical formula at a time. Remove coefficients, reaction arrows, state symbols, and charge notation before calculating.