Grams per Mole to Daltons Converter
Common Conversions
| g/mol | Da |
|---|---|
| 1 | 1 |
| 18.015 | 18.015 |
| 58.44 | 58.44 |
| 100 | 100 |
| 180.16 | 180.16 |
| 342.3 | 342.3 |
| 1000 | 1000 |
| 10000 | 10000 |
| 50000 | 50000 |
| 100000 | 100000 |
| 500000 | 500000 |
| 1000000 | 1000000 |
Why this conversion matters in chemistry
Drug-product molecular weights appear in g/mol on regulatory filings (acetylsalicylic acid 180.16, acetaminophen 151.16, atorvastatin 558.64), and in Da on the corresponding mass-spectrometric identity confirmation. The two notations are numerically equivalent because the gram is defined as Avogadro's number of u. The only refinement that sometimes matters is monoisotopic versus average mass — ASA's average mass is 180.16, but its monoisotopic mass (using ¹²C, ¹H, ¹⁶O exclusively) is 180.0423, which is what an HRMS spectrum actually measures.
Formula
Where the factor comes from
Start from what a dalton actually is: one twelfth of the mass of a free carbon-12 atom at rest in its ground state, roughly 1.660539 × 10⁻²⁴ g. It is a unit of mass, not of molar mass, and it is not an SI unit — it is accepted for use alongside SI, and its value in kilograms has to be measured, since the kilogram is fixed through the Planck constant while the dalton stays tied to a nuclide. It is the same unit as the unified atomic mass unit, u, wearing a second name — and the one that carries SI prefixes in practice, since biochemistry writes kDa and MDa where “ku” never caught on. Its numerical agreement with g/mol runs through the molar mass constant, which sits within about a part in 10⁹ of 1 g/mol — close enough that the two read as one number.
Precision and significant figures
Where this pair actually gets used, precision is instrumental and quoted in parts per million rather than decimal places. An instrument specified at a few ppm resolves something like 0.003 Da on a 600 Da ion and about 0.3 Da on a 60 kDa protein: the absolute error scales with the mass, which is why small-molecule work reports four decimals and protein work reports none. Match your digits to that. A quadrupole running at unit resolution supports whole daltons, and carrying an average molar mass out to four decimals before setting it against such a spectrum implies an agreement the measurement cannot test.
Worked Examples
Water — the textbook reference, where the molar mass and the per-molecule mass match exactly.
Glucose, average mass — the same number on a stoichiometry sheet and a mass-spec result panel.
Bovine serum albumin — the protein-chemistry reference, equivalently 66.5 kDa.
Sucrose — the disaccharide whose molar mass anchors carbohydrate-chemistry calculations.
Common mistakes
Average mass compared with a monoisotopic peak
A high-resolution spectrum reports the monoisotopic mass, built from ¹²C, ¹H, ¹⁶O and their fellow lightest nuclides. A molar mass in g/mol is abundance-weighted. The two diverge by a few tenths of a dalton around 400 to 600 Da and by whole daltons for larger molecules, so a mismatch in the first decimal is usually this rather than a failed synthesis.
m/z on the spectrum is not mass
Electrospray produces multiply charged ions, so a 66 kDa protein appears as a series of peaks near 1660 m/z at forty positive charges, not as a single peak at 66430. A g/mol to Da comparison only means something after deconvolution, and each added proton contributes about 1.007 Da to the measured mass as well.
Salt, solvate and free base confused
The g/mol printed on a bottle usually belongs to the supplied form — a hydrochloride, a hemifumarate, a hydrate — while the neutral mass a spectrum reports belongs to whatever species survived ionization. Comparing the two without first deciding which form each number describes leaves a discrepancy exactly the size of the counterion or the waters of hydration.