g/L to Molarity Converter
Common Conversions
| g/L | M |
|---|---|
| 0.584 | 0.01 |
| 5.844 | 0.1 |
| 9 | 0.154 |
| 29.22 | 0.5 |
| 58.44 | 1 |
| 116.88 | 2 |
| 175.32 | 3 |
| 292.2 | 5 |
| 350.64 | 6 |
| 584.4 | 10 |
| 701.28 | 12 |
Why this conversion matters in chemistry
A balance gives you grams; a titration wants moles. The conversion that connects the two is M = (g/L) / MW, and it's the calculation behind every reagent prep that starts with weighing solute into a volumetric flask. NaCl at 58.44 g/L is exactly 1 M because the molar mass of NaCl is 58.44 g/mol — the convenient coincidence that makes sodium chloride the textbook reference for molarity. Normal saline is 9 g/L of NaCl, which works out to 0.154 M, or 154 mM — the number a clinical-chemistry text writes as 154 mEq/L of Na⁺ since NaCl is a 1:1 electrolyte.
Formula
Where the factor comes from
The divisor is the only interesting part of this one. Molar mass converts grams to moles, and since 2019 the mole has been defined by fixing the Avogadro constant at exactly 6.02214076 × 10²³ per mole — but that exactness does not transfer downward. A compound's molar mass is summed from standard atomic weights, and those are measured quantities. Several are published as intervals rather than single values because natural isotopic composition varies with where the sample came from: chlorine sits near 35.45 and sulfur near 32.06, each uncertain in the second decimal. So M = (g/L) / MW is substance-specific and inexact by construction. The liter underneath is exact, being one cubic decimeter, but it measures finished solution rather than solvent, which quietly makes molarity temperature-dependent.
Precision and significant figures
Molar masses print more digits than any preparation can use. NaCl at 58.44 g/mol offers four figures; the weighing and the flask together rarely support more than three. An analytical balance reading to 0.1 mg against a few grams of solute contributes almost nothing, so the volumetric step dominates — a Class A liter flask is certified to a few hundredths of one percent, and a solution sitting five degrees off that calibration temperature has expanded by roughly a tenth of a percent, several times the flask's own tolerance. Round the molarity to what the weakest step earned, usually three figures. Extra digits pay in one place only: keep the full molar mass through the calculation and round at the end.
Worked Examples
The textbook anchor — sodium chloride at its molar mass per liter is exactly one molar.
Normal saline — 0.9% w/v NaCl, the standard isotonic solution for IV fluids and biochemistry buffers.
One molar sodium hydroxide — convenient because NaOH's molar mass is 39.997 g/mol, close enough to round to 40 in practice.
One molar glucose — a useful reference for any sugar chemistry where mass-based recipes need to land in molarity.
Common mistakes
Hydrate water omitted from the molar mass
Copper sulfate pentahydrate weighs 249.68 g/mol against the anhydrous salt's 159.61. Weigh out the blue crystals, divide by the anhydrous figure, and the molarity comes out 56 percent high — a large enough error to survive as a plausible number rather than an obvious blunder. The dot in CuSO₄·5H₂O belongs in the arithmetic, not just in the name.
Solution volume confused with solvent volume
Molarity is moles per liter of finished solution. Adding solute to a liter of water gives more than a liter of solution, so the actual concentration falls below the intended one — noticeably so for concentrated preparations. Dissolve in a partial volume, then bring to the mark. Molality sidesteps the issue entirely by using solvent mass, which is why it survives temperature changes.
Salt molarity read as ion molarity
Dividing g/L of CaCl₂ by 110.98 g/mol gives the molarity of the salt. The chloride concentration is twice that, and the calcium concentration equals it. Any calculation downstream that wants an ionic strength, a common-ion effect or a charge balance needs the stoichiometric multipliers applied after the conversion, not before.