Molar Mass Calculator

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The molar mass of a compound is the sum of the atomic masses of all its atoms. For sulfuric acid, H₂SO₄: 2(1.008) + 32.06 + 4(15.999) = 98.072 g/mol. Type any formula to see the working, the mass percent of each element, and gram–mole conversions.

FreeStep by stepIUPAC atomic weights

Chemical formula

Brackets and hydrates work: Al2(SO4)3, CuSO4*5H2O. Element symbols start with a capital letter.

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Molar mass of H₂SO₄

\(\displaystyle M\left(\mathrm{H_{2}SO_{4}}\right) = 98.072\ \text{g/mol}\)

One mole of H₂SO₄ has a mass of 98.072 grams.

Share of the molar mass from each element.

Composition by mass
H (Hydrogen): 2 × 1.008	2.016 g/mol · 2.056%
S (Sulfur): 1 × 32.06	32.06 g/mol · 32.69%
O (Oxygen): 4 × 15.999	63.996 g/mol · 65.25%

Show steps

Count the atoms of each element in \(\mathrm{H_{2}SO_{4}}\): H = 2, S = 1, O = 4.
Multiply each count by the element’s atomic mass: \(2 \times 1.008 = 2.016\); \(1 \times 32.06 = 32.06\); \(4 \times 15.999 = 63.996\).
Add them: \(M = 2.016 + 32.06 + 63.996 = 98.072\ \text{g/mol}\).

How to use the molar mass calculator

Type the formula with capital letters for each element, for example NaHCO3 or Mg3(PO4)2.
Press Calculate to get the molar mass in g/mol, a table of each element’s share, and the steps.
To convert, choose Grams to moles or Moles to grams and enter the amount.

Molar mass formula

\(M = \sum (\text{number of atoms of each element}) \times (\text{atomic mass of that element})\)

Atomic masses (standard atomic weights) are in grams per mole. For a bracket with a subscript, multiply everything inside by that subscript: in Ca(OH)₂ there are 2 O and 2 H.

Mass percent of an element \(= \frac{\text{its total mass in the formula}}{M} \times 100\%\).

Worked example: calcium hydroxide

Element	Atoms	Atomic mass	Subtotal	Mass %
Ca	1	40.078	40.078	54.09%
O	2	15.999	31.998	43.19%
H	2	1.008	2.016	2.72%
Total			74.092 g/mol	100%

25 g of Ca(OH)₂ is \(\frac{25}{74.092} \approx 0.3374\) mol.

Grams, moles and particles

\(n = \frac{m}{M}\) (moles = mass ÷ molar mass)
\(m = n \times M\) (mass = moles × molar mass)
Number of particles \(= n \times N_{A}\), with Avogadro’s number \(N_{A} = 6.02214076 \times 10^{23}\ \text{mol}^{-1}\)

Molar masses of common substances

Substance	Formula	Molar mass (g/mol)
Water	H₂O	18.015
Carbon dioxide	CO₂	44.009
Sodium chloride	NaCl	58.44
Glucose	C₆H₁₂O₆	180.156
Sulfuric acid	H₂SO₄	98.072
Ammonia	NH₃	17.031
Oxygen gas	O₂	31.998

Values use IUPAC standard atomic weights (conventional values for elements whose weight varies in nature, such as H = 1.008 and S = 32.06). Some textbooks round differently, so the last decimal can differ slightly.

Molar mass practice quiz: 10 questions

Test yourself with 10 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.

Frequently asked questions

How do you calculate molar mass?

Count the atoms of each element in the formula, multiply each count by that element’s atomic mass, and add the results. The answer is in grams per mole.

Is molar mass the same as molecular weight?

They have the same number. Molecular weight (relative molecular mass) has no units; molar mass is the same value in g/mol.

Which atomic masses does the calculator use?

IUPAC standard atomic weights, using the conventional values for elements whose weight varies in nature. For radioactive elements with no standard weight, the mass number of the most stable isotope is used and marked.

How do I convert grams to moles?

Divide the mass in grams by the molar mass: n = m ÷ M. Choose Grams to moles in the calculator to do it for you.

How do I enter a hydrate?

Use * or ·, for example CuSO4*5H2O. The 5 multiplies the whole water unit.

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