Universal Mass to Molar Unit Converter
Universal Mass to Molar Unit Converter
Convert mg/dL, mg/L, µg/mL, g/L and g/dL to mmol/L for any analyte, by entering its molecular weight rather than looking up a factor. The arithmetic is one line; the two places it goes wrong — urea against BUN, and triglycerides — are the reason this page is longer than the formula.
mg/dL to mmol/L, any analyte
Mass + MW → mmol/LGlucose 100 mg/dL, molecular weight 180.156 g/mol
The formula, and where it comes from
mg/dL = mmol/L × molecular weight ÷ 10
because 1 mg/dL is 0.01 g/L, and 0.01 ÷ MW mol/L = (10 ÷ MW) mmol/L
- × 10 ÷ MW
- the whole conversion. One milligram per decilitre is 0.01 grams per litre; divide by grams per mole to get moles per litre; multiply by 1,000 for millimoles. The 0.01 and the 1,000 collapse to 10
- molecular weight
- grams per mole of the molecule the assay measures. Not the salt it was weighed out as, not a subunit, and not an average of a family of molecules — see the two warnings below
- mg/L, µg/mL
- the same concentration written two ways, and a tenth of the mg/dL figure. One milligram in a litre is one microgram in a millilitre; there is no factor between them at all
- g/L and g/dL
- g/L is 100 mg/dL and g/dL is 1,000 mg/dL. These are the units protein results arrive in, and a g/dL read as g/L is a tenfold error
- what this cannot do
- a unit conversion needs one molecule and one mass. It cannot cross between a mass and an international unit, it cannot convert a nitrogen content into the compound that contained it, and it cannot handle a mixture. Those are the next two sections
Worked example
Glucose 100 mg/dL, molecular weight 180.156 g/mol
100 mg/dL = 1.00 g/L
1.00 ÷ 180.156 = 5.5507 × 10⁻³ mol/L = 5.551 mmol/L
The same thing in one step: 100 × 10 ÷ 180.156 = 5.551
That agrees with the factor of 0.0555074 on the dedicated glucose converter, because it is the same arithmetic — and that page is still the better one to use, because it also carries the diagnostic thresholds
The molecular weights you will actually need
| Analyte | Molecular weight (g/mol) | mg/dL → SI | Its own page |
|---|---|---|---|
| Glucose (C₆H₁₂O₆) | 180.156 | × 0.055507 → mmol/L | glucose converter |
| Cholesterol — total, LDL, HDL or non-HDL (C₂₇H₄₆O) | 386.65 | × 0.025863 → mmol/L | cholesterol converter |
| Creatinine (C₄H₇N₃O) | 113.12 | × 88.402 → µmol/L | creatinine converter |
| Urea (CH₄N₂O) — see the warning below | 60.06 | × 0.16651 → mmol/L | urea and BUN converter |
| Bilirubin (C₃₃H₃₆N₄O₆) | 584.66 | × 17.104 → µmol/L | bilirubin converter |
| Uric acid or urate (C₅H₄N₄O₃) | 168.11 | × 59.485 → µmol/L | uric acid converter |
| Calcium (Ca) | 40.078 | × 0.24951 → mmol/L | calcium converter |
| Triglyceride, as triolein — see the warning below | 885.4 | × 0.011294 → mmol/L | triglyceride converter |
Urea and BUN: not a unit conversion
| Quantity | What it counts | Molar mass used | Conversion |
|---|---|---|---|
| Urea, mg/dL | The whole urea molecule, CH₄N₂O | 60.06 | × 0.16651 → mmol/L urea |
| Blood urea nitrogen (BUN), mg/dL | Only the two nitrogen atoms in it | 28.014, i.e. 2 × 14.007 | × 0.35696 → mmol/L urea |
| BUN → urea, both in mg/dL | The same substance, differently counted | 60.056 ÷ 28.014 | × 2.1438, usually quoted as × 2.14 |
| Urea → BUN, both in mg/dL | The reverse | 28.014 ÷ 60.056 | × 0.4665, usually quoted as ÷ 2.14 |
Triglycerides: no single molecular weight exists
| Triacylglycerol | Formula | Formula mass | mg/dL → mmol/L would be |
|---|---|---|---|
| Triolein — the conventional assumption | C₅₇H₁₀₄O₆ | 885.45 | × 0.011294 |
| Trilinolein | C₅₇H₉₈O₆ | 879.41 | × 0.011371 |
| Tripalmitin | C₅₁H₉₈O₆ | 807.34 | × 0.012386 |
| Trimyristin | C₄₅H₈₆O₆ | 723.18 | × 0.013828 |
One formula, and the two things it cannot do
Mass concentration counts grams and molar concentration counts molecules, and the only thing standing between them is how much a mole of the substance weighs. That makes the conversion trivial once you have the molecular weight: one milligram per decilitre is one hundredth of a gram per litre, dividing grams per litre by grams per mole gives moles per litre, and a thousand millimoles make a mole. The three steps collapse into multiplying the mg/dL figure by ten and dividing by the molecular weight. Every published mass-to-molar factor in laboratory medicine — 0.0555 for glucose, 0.0259 for cholesterol, 88.4 for creatinine — is that one line with a different number in it.
Which raises a fair question about why this site carries more than two hundred analyte-specific converters. The answer is that the factor is the least useful thing a converter can give you. A creatinine of 88 µmol/L is meaningless without knowing that the adult interval runs to about 110, that it depends on muscle mass, and that the number feeding an eGFR equation has to be the one the equation was calibrated against. So if the analyte you are holding has its own page — and the table above links eight of the commonest — use that page. This one is for the analyte that does not: a research measurand, an uncommon metabolite, a drug nobody has written a page about.
There are two situations where entering a molecular weight gives a confidently wrong answer, and they are the reason a universal converter is dangerous when used without reading anything. The first is blood urea nitrogen. BUN and urea are not two units for one quantity; BUN reports only the nitrogen in the urea, so converting it needs a stoichiometry as well as a mass. Urea is CH₄N₂O and carries two nitrogen atoms, so its formula mass of 60.056 is 2.1438 times the 28.014 of the nitrogen it contains — which is where the familiar factor of 2.14 comes from, and why it is arithmetic on atomic weights rather than a measured constant. Feed a BUN into this tool with urea’s weight of 60.06 and every answer will be more than twice too small.
The second is triglycerides, and it is worse because there is nothing to correct. A serum triglyceride is a mixture of triacylglycerols whose fatty-acid chains vary with diet, metabolism and the individual, so there is no molecular weight to enter. The conventional factor of 0.0113 comes from treating the whole mixture as triolein, formula mass 885.45, and its reciprocal is 88.54. That convention is worth following because it makes results comparable, but a triglyceride reported in mmol/L is a nominal molar concentration, not a count of molecules. The wider lesson generalises: a molar unit is only as meaningful as the claim that the measurand has one mass. Glycoproteins, immunoglobulins and anything standardised against an international unit fail that test, which is why the site’s converters for those analytes offer no molar unit at all rather than offering a plausible one.
Frequently asked questions
How do I convert mg/dL to mmol/L?
Multiply by 10 and divide by the molecular weight. A glucose of 100 mg/dL is 100 × 10 ÷ 180.156 = 5.55 mmol/L; a cholesterol of 200 mg/dL is 200 × 10 ÷ 386.65 = 5.17 mmol/L. There is no single factor from mg/dL to mmol/L, which is why the question needs the analyte before it has an answer.
Is there one conversion factor from mg/dL to mmol/L?
No, and that is the commonest misconception about these units. The factor is 10 divided by the molecular weight, so it differs for every analyte: 0.0555 for glucose, 0.0259 for cholesterol, 0.2495 for calcium and 0.0113 for triglyceride. Using one analyte’s factor for another is not a rounding error — glucose and cholesterol differ by more than twofold.
Can I convert BUN to urea with this?
Not directly, because BUN is not urea. BUN measures only the nitrogen, and urea contains two nitrogen atoms out of a formula mass of 60.056, so urea in mg/dL is BUN in mg/dL × 2.1438. If your report says BUN, enter 28.014 as the molecular weight and you will get millimoles of urea per litre; if it says urea, enter 60.06.
Why does a triglyceride need a different factor from cholesterol?
Because it is a different and much heavier molecule: cholesterol is 386.65 g/mol and a triglyceride is taken as about 885 g/mol. Converting a triglyceride with the cholesterol factor overstates it by well over twofold. Worse, triglyceride has no true single molecular weight, because serum triglyceride is a mixture of chain lengths and 885.45 is an assumption about its average.
Should I use this or the analyte’s own converter?
Its own converter, wherever one exists. The factor is identical — this tool and the dedicated pages run the same arithmetic on the same molecular weights — but the dedicated page also carries the reference interval, the thresholds and the assay caveats, and those are what turn a converted number into a usable one.
Which molecular weight should I enter for a drug or a salt?
The one for the species the assay measures, which is usually the free base or free acid rather than the salt. A formula weight that includes a chloride, a sodium or water of crystallisation will give a molar concentration that is too low, because part of the mass you divided by was never in the patient.
Related calculators
References
- Bureau International des Poids et Mesures. The International System of Units (SI Brochure). 9th ed. — the definition of the mole and of amount-of-substance concentration.
- Commission on Isotopic Abundances and Atomic Weights (IUPAC). Standard atomic weights. Every molecular weight tabled here was recomputed from its formula using C 12.011, H 1.008, N 14.007 and O 15.999.
- Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier; 2018 — units of measurement, and the urea/BUN relationship.
- National Center for Biotechnology Information. PubChem Compound Summary for CID 5497163, triolein (C₅₇H₁₀₄O₆), and CID 11147, tripalmitin (C₅₁H₉₈O₆).
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.