Grams to Moles Converter
Common Conversions
| g | mol |
|---|---|
| 1 | 0.05551 |
| 5 | 0.2775 |
| 10 | 0.5551 |
| 18.015 | 1 |
| 25 | 1.388 |
| 36.03 | 2 |
| 50 | 2.775 |
| 100 | 5.551 |
| 180.15 | 10 |
| 500 | 27.75 |
| 1000 | 55.51 |
Why this conversion matters in chemistry
Every yield calculation starts with this step. You've isolated something — a crude product, a purified precipitate, a dried recrystallization — and the balance gives you a mass. To compare against the reaction stoichiometry, or a limiting reagent, you need moles, which means dividing by the molar mass. 1.87 g of crude aspirin (MW 180.16) divided out is 0.01038 mol — the number every percent-yield calculation eats as input. Gravimetric analysis does the same move in the other direction: weigh the precipitate, convert to moles, read off the analyte content. The mass number is what the experiment gives you; the mole number is what tells you what actually happened.
Formula
Where the factor comes from
Nothing on this page is a unit conversion in the strict sense. Grams measure mass, moles measure amount of substance, and the only bridge between them is the molar mass of one particular compound — so the factor changes every time the substance does. Molar mass is assembled by summing standard atomic weights across the formula, and those weights are measured, not defined. Several are published as intervals rather than single values because the isotopic composition of ordinary terrestrial material genuinely varies: sulfur spans 32.059 to 32.076, a few hundredths of a percent, while lithium runs from 6.938 to 6.997 — most of a percent on its own. A second inexactness arrived in 2019, when the molar mass constant stopped being exactly 1 g/mol, though at a few parts in 10¹⁰ that one will never reach your answer.
Precision and significant figures
The balance normally sets the ceiling. A four-place analytical balance reading 1.8734 g offers five figures, glucose at 180.16 g/mol offers five, and 0.010398535 mol truncates honestly to 0.010399 mol. Carry the full calculator display through a multi-step yield calculation so rounding cannot accumulate, then stop the reported answer where the weaker input stopped. Elements with wide tabulated intervals are the exception worth watching: a formula heavy in lithium, sulfur or boron may not support a fourth figure in its molar mass however good the weighing was. Sub-milligram samples move the limit again, and there the microbalance rather than the arithmetic is the constraint.
Worked Examples
A mole of water. About a tablespoon, and the reference point most of us check numbers against.
Enough salt for 100 mL of 1 M NaCl. The kind of thing you end up weighing two or three times a week if you're prepping buffers.
A mole of sulfuric acid. You'd almost never measure it by mass — it's a dense, viscous liquid you pipette by volume — but the number is useful to know.
A mole of carbon atoms. Back when the mole was defined from carbon-12, this was literally the anchor that tied macroscopic mass to atomic count across the whole SI system.
Common mistakes
Hydrate water left out of the molar mass
Copper(II) sulfate pentahydrate is 249.68 g/mol; the anhydrous salt is 159.60. Divide a mass of the blue pentahydrate by the anhydrous figure and the mole count comes out 56 percent high. The bottle label carries the hydration state, the compound name in a procedure often does not, and a solid that has sat in a humid room may not match either number cleanly.
Salt form on the label, free base assumed
Amines, carboxylic acids and many building blocks ship as hydrochlorides, sodium salts or acetates. The molar mass on the certificate belongs to the salt, while a procedure quoting a concentration usually means the free base. Weigh the salt, divide by the free-base molar mass, and the mole figure inflates by the difference — for a small amine hydrochloride, comfortably more than ten percent.
Assay purity treated as one hundred percent
A reagent certified at 97 percent means 1.000 g of powder holds 0.97 g of the compound, so dividing the gross mass by molar mass leaves the mole figure three percent high before anything reacts. Hygroscopic solids err the same way from the opposite direction, gaining mass that is water and contributes nothing to the amount actually charged.