- 01There is no universal mg/dL to mmol/L conversion
Each substance converts by its own fixed factor, because mg/dL weighs the molecules and mmol/L counts them, and different molecules weigh different amounts. Glucose divides by 18, cholesterol by 38.67, and triglycerides by 88.5, three numbers on one panel. Searching for one magic factor fails.
Your lab report prints numbers in units you were probably never taught to read, and the same test can show a completely different number depending on where it was run. A US lab reports a fasting glucose as 100 mg/dL; a lab in London reports the identical measurement as 5.6 mmol/L. Before you compare your result to anything, you need to know which units it was written in, and right after that, which reference range it is read against.
What to do next: find the units printed next to each value on your report, usually in small type right after the number. If you want to compare against a range or an old result written in other units, convert with the factors below. Bring anything flagged high or low to your clinician instead of acting on it yourself.
What mg/dL and mmol/L mean
mg/dL means milligrams per deciliter. A deciliter is 100 mL, one-tenth of a liter, so mg/dL is a mass concentration: how much of a substance, by weight, sits in a fixed volume of blood.1 It is the conventional unit on most US reports for glucose, cholesterol, and creatinine (a waste product used to gauge kidney function).
mmol/L means millimoles per liter. A mole is a fixed count of molecules, so mmol/L is a molar concentration: how many molecules, rather than how many milligrams, sit in a liter of blood.1 Most countries outside the US report in mmol/L, the SI unit (SI being the international metric standard used across science). The two units describe the same blood, one by weight and one by number.
Why there is no single conversion factor
To turn a weight into a count of molecules, you divide by a factor built from the molecule's weight, how much one mole of it weighs, then adjusted for the deciliter-to-liter step, which works out to roughly a tenth of its molecular weight.1 Heavy molecules give big divisors; light ones give small divisors. Glucose is a small molecule, molecular weight around 180, so you divide by 18. A cholesterol molecule is heavier, around 387, so you divide by 38.67. A triglyceride is heavier still, so you divide by about 88.5. That is why one magic number can never convert a whole report, and why the glucose and the cholesterol on the same page use different factors.
Convert the results you meet most
Here are the tests people most often need to move between the two systems. To go from US mg/dL to the SI unit, divide by the factor in the fourth column; to go the other way, multiply.1
| Test | US units | Rest-of-world units (SI) | Convert mg/dL to SI | Worked example |
|---|---|---|---|---|
| Glucose | mg/dL | mmol/L | ÷ 18 | 100 mg/dL = 5.6 mmol/L |
| Total cholesterol | mg/dL | mmol/L | ÷ 38.67 | 200 mg/dL = 5.2 mmol/L |
| LDL cholesterol | mg/dL | mmol/L | ÷ 38.67 | 100 mg/dL = 2.6 mmol/L |
| HDL cholesterol | mg/dL | mmol/L | ÷ 38.67 | 50 mg/dL = 1.3 mmol/L |
| Triglycerides | mg/dL | mmol/L | ÷ 88.5 | 150 mg/dL = 1.7 mmol/L |
| Creatinine | mg/dL | µmol/L | × 88.4 | 1.0 mg/dL = 88 µmol/L |
| HbA1c | % (NGSP) | mmol/mol (IFCC) | see below | 6.5% = 48 mmol/mol |
Creatinine is the odd one out in the table: it converts to µmol/L, micromoles per liter, because it circulates at far smaller amounts than glucose or cholesterol, so it is counted in micromoles, a thousandth of a millimole.
- 1Read the units off the reportFind the small unit label after the number, such as mg/dL or mmol/L. If two reports use different units, they are not directly comparable until you convert one of them.
- 2Pick the factor for that testUse the factor for that specific substance from the table above, not a generic one. Glucose, cholesterol, and triglycerides each have their own.
- 3Divide to reach SI, multiply to come backmg/dL divided by the factor gives mmol/L. mmol/L times the factor gives mg/dL. A glucose of 5.6 mmol/L times 18 is about 100 mg/dL.
Why US and European numbers look different
Because the US reports in mg/dL and most of the world in mmol/L, the same clinical target is written as two different-looking numbers. US cholesterol guidance talks about an LDL (low-density lipoprotein, the artery-clogging cholesterol) under 100 mg/dL; European guidance for the same risk level talks about an LDL under 2.6 mmol/L.6 Those are the same goal in different units. An old report from a US lab and a new one from a European lab can look wildly different for no medical reason at all.
A few tests need no conversion at all: TSH (thyroid-stimulating hormone) is written in mIU/L (milli-international units per liter), which is numerically identical to µIU/mL, so a TSH reads the same on a US or an international report.1
A lab number means nothing until it carries two labels: the unit it was measured in and the reference range it is read against.
Converting a number gets it into the right units, but units are not the same as normal. The same 5.0 is a healthy fasting glucose in mmol/L, far outside range for a potassium, and mid-range for a total cholesterol. To read whether a value is in range, see reference ranges explained.
HbA1c travels under two units
HbA1c, the three-month average of your blood sugar, has its own two-unit split. US labs report it as a percentage on the NGSP scale (National Glycohemoglobin Standardization Program); most of Europe reports it in mmol/mol on the IFCC scale (International Federation of Clinical Chemistry). The master equation is IFCC = (NGSP% - 2.15) x 10.929, so an HbA1c of 6.5% is 48 mmol/mol and 5.7% is about 39 mmol/mol.4
People also convert HbA1c into an estimated average glucose (eAG), the everyday glucose number it corresponds to. The regression comes from the ADAG study:
eAG(mg/dL) = 28.7 x A1C - 46.7Nathan DM et al, Translating the A1C Assay Into Estimated Average Glucose Values, Diabetes Care 2008
By that formula an HbA1c of 7% is an average glucose of about 154 mg/dL (8.6 mmol/L), and 6% is about 126 mg/dL.2
Enter your own HbA1c to see it as an average glucose in both unit systems:
What your A1c means in daily glucose
Your HbA1c, translated to an average glucose. Nothing leaves your browser.
Two traps where a naive conversion misleads
BUN measures only part of the urea molecule
US labs report blood urea nitrogen (BUN), which counts only the nitrogen inside the urea molecule; most other countries report whole urea. That makes it a change of measurand, the actual quantity being measured, on top of the change of units. To convert, urea in mmol/L equals BUN in mg/dL times 0.357, and urea in mg/dL equals BUN times 2.14.1 Push a BUN through a glucose-style factor and you get a number that means nothing.
Lp(a) has no dependable conversion
Lp(a) (lipoprotein little-a), an inherited cholesterol-like particle that raises heart-attack and stroke risk, is reported either as a mass in mg/dL or as a particle count in nmol/L. Those two units measure different things, and the relationship between them shifts with the size of the particle, so no fixed factor is reliable.5 Applying one anyway can move a result across a risk cutoff in either direction. The European Atherosclerosis Society advises reporting the unit the assay was calibrated to rather than converting between them.5
So if your Lp(a) sits near a risk cutoff, the same sample can fall on either side of that line depending on which unit and assay were used. Read it as a band rather than one converted number, and check your report for whether the value is in mg/dL or nmol/L before comparing it to any range.5
Citations
- Young DS. Implementation of SI Units for Clinical Laboratory Data: Style Specifications and Conversion Tables. Annals of Internal Medicine. 1987;106(1):114-129.
- Nathan DM, Kuenen J, Borg R, Zheng H, Schoenfeld D, Heine RJ; A1c-Derived Average Glucose Study Group. Translating the A1C Assay Into Estimated Average Glucose Values. Diabetes Care. 2008;31(8):1473-1478.
- American Diabetes Association. Standards of Care in Diabetes 2025: Classification and Diagnosis of Diabetes. Diabetes Care. 2025;48(Suppl 1).
- National Glycohemoglobin Standardization Program (NGSP). HbA1c NGSP to IFCC conversion and master equation.
- Kronenberg F, Mora S, Stroes ESG, et al. Lipoprotein(a) in atherosclerotic cardiovascular disease and aortic stenosis: a European Atherosclerosis Society consensus statement. European Heart Journal. 2022;43(39):3925-3946.
- Mach F, Baigent C, Catapano AL, et al. 2019 ESC/EAS Guidelines for the management of dyslipidaemias. European Heart Journal. 2020;41(1):111-188.
Educational context only, not medical advice or a diagnosis. Always discuss your results with a clinician.