QUICK PEEKMOLAR MASS CALCULATOR

Molar mass calculator: formula to g/mol and % composition.

Type a chemical formula and get its molar mass in g/mol: each element's standard atomic weight times its count, added up, plus each element's percentage by mass. Brackets, nested groups and hydrates like CuSO₄·5H₂O all work.

Calculate a molar mass All quick peeks

NO ACCOUNT · RUNS IN YOUR BROWSER · ABOUT 30 SECONDS

Fig 0CAFFEINE · C₈H₁₀N₄O₂ · 194.19 g/mol

Caffeine, C₈H₁₀N₄O₂: 194.19 g/mol. It's the pre-filled example below.

FIG 1THE PEEK

Type a formula, read the breakdown.

Caffeine is pre-filled. Change it, or pick one of the examples.

Fig 1FORMULA → g/mol · MASS %

CHEMICAL FORMULA

BRACKETS ( ) [ ] NEST · HYDRATES WITH · OR * OR . · CASE MATTERS: Co ≠ CO

TRY AN EXAMPLE

C₈H₁₀N₄O₂

THE LINK CONTAINS YOUR INPUTS AND REOPENS THIS RESULT

194.19 g/mol

MOLAR MASS

194.191

TO 3 DP · g/mol

ATOMS PER FORMULA UNIT

COMPOSITION BY MASS

ELEMENT	COUNT	ATOMIC WT	MASS	MASS %
C	8	12.011	96.086	49.48%
H	10	1.008	10.079	5.19%
N	4	14.007	56.027	28.85%
O	2	15.999	31.999	16.48%
Total			194.191	100.00%

Masses in g/mol. Standard atomic weights (IUPAC 2007 values, as printed in most textbooks); your course's data sheet may round differently.

RUNS ENTIRELY IN YOUR BROWSER — NOTHING IS UPLOADED.

FIG 2HOW TO USE

How to use the molar mass calculator

01 →
Type the formula
Case matters: Co is cobalt, CO is carbon monoxide. Use brackets for groups, Ca3(PO4)2, and ·, * or a full stop for hydrates, CuSO4·5H2O.
02 →
Read the molar mass
The total in g/mol appears as you type, to two and three decimal places, with the number of atoms per formula unit.
03
Check the breakdown, then share
The table lists each element's count, atomic weight, mass and mass %. Copy the mass, or share a link that reopens this exact result.

MethodWHAT THE CODE DOES

How it works: the method

The calculator reads the formula into a count of atoms per element, then adds up count × standard atomic weight:

M = Σ nᵢ × Aᵣ(i)      (g/mol)
mass %ᵢ = nᵢ × Aᵣ(i) / M × 100

A number after a closing bracket multiplies everything inside it, and brackets can be nested. A formula split by a hydrate dot is read part by part, and a leading number multiplies only its own part, so ·5H2O adds 10 H and 5 O.

Atomic weights are the IUPAC 2007 standard atomic weights (H 1.00794, C 12.0107, N 14.0067, O 15.9994, Na 22.98976928, S 32.065, Cl 35.453, Cu 63.546). The total is shown rounded to 2 and 3 decimal places, rounding halves away from zero.

ExampleCAFFEINE · C8H10N4O2

Worked example

Caffeine has 8 carbon, 10 hydrogen, 4 nitrogen and 2 oxygen atoms:

C   8 × 12.0107  = 96.0856
H  10 × 1.00794  = 10.0794
N   4 × 14.0067  = 56.0268
O   2 × 15.9994  = 31.9988
──────────────────────────
M = 194.1906 ≈ 194.19 g/mol

By mass that is C 49.48%, H 5.19%, N 28.85% and O 16.48%. For a hydrate, CuSO4·5H2O counts Cu 1, S 1, O 9 and H 10, giving 249.685, shown as 249.69 g/mol.

FIG 3THE FULL WORKSPACE

What the full workspace adds.

Fig 3IN MOREMIND

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FIG 4QUESTIONS

Molar mass: common questions

Which atomic weights does the calculator use?

Standard atomic weights as published by IUPAC in 2007, the values most textbooks and data sheets still print: for example H 1.00794, C 12.0107, N 14.0067, O 15.9994, S 32.065 and Cl 35.453. Newer IUPAC tables give some elements as ranges or abridged values, so results can differ from other calculators in the second decimal place. If your course gives a data sheet, use its values for marked work.

How do you calculate molar mass by hand?

Count the atoms of each element in one formula unit (multiplying through any brackets and hydrate coefficients), multiply each count by that element's atomic weight, and add the products. The sum is the molar mass in grams per mole. For water, H2O: 2 × 1.00794 + 15.9994 = 18.01528, so 18.02 g/mol.

How is percentage composition worked out?

Each element's mass in the formula (count × atomic weight) is divided by the molar mass and multiplied by 100. The percentages add up to 100% apart from rounding.

What formulas can it read?

Element symbols with counts, round, square or curly brackets nested to any depth, and hydrates or adducts joined with ·, * or a full stop, each with an optional leading coefficient (e.g. Na2CO3·10H2O). Subscript digits such as C₆H₁₂O₆ and condensed formulas such as CH3CH2OH work too. It doesn't read charges, isotopes, state symbols or bond characters.

Which elements are included?

69 elements: everything from hydrogen to xenon except technetium, plus Cs, Ba, La, Ce, Nd, Gd, W, Os, Ir, Pt, Au, Hg, Tl, Pb, Bi and U. Any other symbol gives an "Unknown element" message rather than a wrong answer.

Is my formula uploaded or stored?

No. The calculation runs in your browser. If you press Share result, the formula is written into the link itself, so anyone who opens the link (and our server, which draws the page and its preview image) sees the formula. Nothing is saved to an account.

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