Molarity to g/L Converter
Common Conversions
| M | g/L |
|---|---|
| 0.001 | 0.058 |
| 0.01 | 0.584 |
| 0.05 | 2.922 |
| 0.1 | 5.844 |
| 0.25 | 14.61 |
| 0.5 | 29.22 |
| 1 | 58.44 |
| 2 | 116.88 |
| 5 | 292.2 |
| 10 | 584.4 |
| 12 | 701.3 |
Why this conversion matters in chemistry
A protocol calls for 137 mM NaCl in a phosphate-buffered saline; a balance can only weigh in grams. Multiplying molarity by molar mass closes that gap. NaCl at 0.137 M and 58.44 g/mol comes out to 8.01 g per liter — the value that goes onto the prep sheet for a Western-blot transfer buffer or a cell-culture wash. The conversion is the standard step every wet-lab buffer preparation runs through, and the reason a chemistry stockroom keeps molar masses written next to the bottles.
Formula
Where the factor comes from
Neither the gram nor the liter depends on an artifact any more. The gram descends from the kilogram, fixed since 2019 through an exact value of the Planck constant, and the liter has been exactly one cubic decimeter since the CGPM settled the matter in 1964. That second date carries more weight than it appears to: between 1901 and 1964 the liter was defined as the volume of one kilogram of water at its density maximum, making it 1.000028 dm³, some 28 parts per million larger than the modern one. Concentrations from that era carry the offset harmlessly. Everything inexact in g/L = M × MW therefore sits in the molar mass, summed from standard atomic weights that are measured values and, for several elements, published as ranges.
Precision and significant figures
Four to six digits in a molar mass, three or four out of the volumetric glassware, and a four-place balance comfortably better than either. The mismatch deserves a sentence because this is the prep direction, where the mass is a target rather than a result. Weighing a target of 8.01 g of sodium chloride onto a balance reading 8.0134 g means the solution's actual concentration is that weighed mass over the molar mass, and the back-calculated figure is the one to record when the preparation has to be traceable. Hygroscopic solids sharpen the point. Sodium hydroxide pellets and calcium chloride take up water from the air while the balance door stands open, so the weighed mass overstates the solute and the delivered concentration lands low.
Worked Examples
One molar sodium chloride — the canonical reference, since NaCl's molar mass is the textbook example.
A dilute sodium hydroxide working solution — useful for a quick titration or a pH adjustment.
Half-molar glucose — about 9% w/v, a common concentration in cell-culture media.
Concentrated hydrochloric acid for stripping, dissolution, or aggressive cleaning — the working dilution from a 12 M stock.
Common mistakes
Stated assay changes the mass required
The product of molarity and molar mass is the mass of pure compound required. A reagent assaying at 97 percent, or a lyophilized protein whose certificate reports 80 percent protein by weight with the balance as buffer salts, calls for that mass divided by the mass fraction. Skip the division and every solution made from the lot is dilute by the same few percent, consistently and invisibly.
Concentrated acids are never weighed
Six molar hydrochloric acid works out to 218.8 g of HCl per liter, but nobody puts that on a balance. It arrives as a solution near 37 percent by mass at a density around 1.18 g/mL, so turning the g/L figure into a volume needs both numbers. That step is a density calculation wearing a unit conversion's clothing, and the bottle's stated strength is a specification range.
Grams per liter read as a percentage
A 58.44 g/L solution is 5.844 percent w/v, since percent weight-per-volume counts grams per 100 mL rather than per liter. Losing that factor of ten is easy because both notations describe the same preparation and look equally reasonable. Percent w/w is a further step away again: it is a mass ratio, and reconciling it with either of the others requires the solution's density.