Molar Mass Calculator
Molecular mass from a written formula
Type any formula with brackets and hydrates; get molar mass, per-element breakdown and percentage composition.
Molar Mass Calculator
Runs in your browser · nothing uploadedMass contribution · O · Cu · S · H. Bar chart with 4 steps across the term, falls from 57.670910816775276% at the first step, to 12.840590042334696% at the midpoint, to 4.037216083179468% by the final step.
| Element | Count | Mass | Share |
|---|---|---|---|
| O · Oxygen | 9 | 143.9910 | 57.67% |
| Cu · Copper | 1 | 63.5460 | 25.45% |
| S · Sulfur | 1 | 32.0600 | 12.84% |
| H · Hydrogen | 10 | 10.0800 | 4.04% |
01 — How to use Molar Mass Calculator
02 — Getting good results
03 — Questions
No. The element table is built into the page and the parsing is done in this browser tab. There is no lookup service involved.
IUPAC standard atomic weights — the natural-abundance averages. Where IUPAC publishes an interval rather than a single figure, because isotopic composition varies measurably by source as it does for carbon and lithium, the conventional value is used. That is what a formula weight is normally expected to be.
Elements with no stable isotope have no meaningful natural-abundance average, so the figure used is the mass number of the longest-lived isotope. That is a different kind of quantity, and any formula containing one is flagged rather than presented with false precision.
Not currently. It parses neutral formulas with brackets and hydrates. Charge notation like SO4^2- and isotope notation like 13C are not supported, and are rejected rather than silently ignored.
04 — More about Molar Mass Calculator
What a molar mass actually is
A molar mass is the mass of one mole — 6.02214076 × 10²³ formula units — of a substance, expressed in grams per mole. Its numerical value equals the formula weight in atomic mass units, which is why the calculation is simply the sum of the constituent atomic weights. The subtlety is in those atomic weights: they are not the mass of a single atom of the element, but a weighted average across the isotopes found in nature. Chlorine's 35.45 reflects a mixture of roughly three parts chlorine-35 to one part chlorine-37; no individual chlorine atom weighs 35.45. For ordinary laboratory work that average is exactly what you want, because any real sample contains the natural mixture. It becomes wrong only when working with isotopically enriched material, which is why isotope-specific calculation is a separate problem rather than a setting.
Parsing a formula correctly
Chemical formula notation is compact and genuinely ambiguous to a naive parser. Symbols are one or two letters and the second is lowercase, so a greedy match reading two characters at a time turns CO into cobalt rather than carbon and oxygen — the fix is to try the longer symbol first and fall back when it is not a real element. Brackets nest arbitrarily and their multipliers compound, so K4(Fe(CN)6) must yield six carbons and six nitrogens rather than one of each. Hydrate dots introduce a second kind of multiplier that applies to an entire following group. Each of these is a small rule, and getting any one wrong produces a plausible-looking number rather than an obvious failure, which is why the test suite here checks specific formulas against published values rather than only checking that the parser does not crash.
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