Laboratory results for blood glucose are reported in mg/dL in some countries and mmol/L in others, and the conversion runs through the molar mass: mmol/L = mg/dL × 10 ÷ 180.156, which for glucose is a factor of 0.0555074. A reference interval of 70–100 mg/dL is therefore 3.886–5.551 mmol/L, the same interval in different clothes.
The figure comes from the formula. Glucose is 6 × 12.011 (C) + 12 × 1.008 (H) + 6 × 15.999 (O), which is 180.156 g/mol, taking standard atomic weights, and every page here computes that sum rather than quoting it. Oxygen makes up the largest share of the mass: 6 of the 24 atoms in a formula unit are oxygen, and they account for 95.994 g of the 180.156 g, or 53.28% by mass. The derivation table below breaks the whole molecule down element by element.
The factor is specific to the substance being measured, which is why a single "divide by 18" cannot be applied across a report: that figure belongs to glucose alone. For glucose the divisor is 18.0156, and using the wrong one produces a number that looks plausible and is wrong by a factor of two or three — the commonest error in reading a foreign result.
Blood sugar, dextrose in the kitchen and the standard carbon source in microbiology. Labs report it in mg/dL in the US and mmol/L elsewhere. At 180.156 g/mol it is heavier than 15 of the 21 organic compounds covered here, and that ranking matters more than it looks: uric acid has a molar mass of 168.112 g/mol, so a gram of it contains 7.16% more formula units than a gram of glucose. Weigh by mass and you are not weighing equal amounts of substance.
Purity is the usual gap between the calculation and the balance. A reagent sold at 98% means 3.6031 g of a nominal 180.156 g is something else, so for exact work you divide the weighed mass by the assay figure on the certificate. For most purposes the difference is smaller than the error in reading the meniscus, but it is systematic rather than random, so it does not average out.
The formula
mg/dL- The reported result in milligrams per decilitre
180.156- The molar mass of glucose in g/mol, derived from its formula
mmol/L- The same result in millimoles per litre
How it works, step by step
- Enter the result as reported, in mg/dL.
- It is multiplied by 10 to give mg/L.
- That is divided by 180.156 g/mol to give mmol/L.
- The reference interval is shown in both units so the converted figure can be read against it.
Worked examples
70 mg/dL of blood glucose in mmol/L
70 × 0.0555074 = 3.8855 mmol/L, which is 3885.5 µmol/L. That result is at the bottom of the quoted interval of 70–100 mg/dL, or 3.886–5.551 mmol/L in the other unit.
85 mg/dL of blood glucose in mmol/L
85 × 0.0555074 = 4.7181 mmol/L, which is 4718.1 µmol/L. That result is in the middle of the quoted interval of 70–100 mg/dL, or 3.886–5.551 mmol/L in the other unit.
140 mg/dL of blood glucose in mmol/L
140 × 0.0555074 = 7.771 mmol/L, which is 7771 µmol/L. That result is above the quoted interval of 70–100 mg/dL, or 3.886–5.551 mmol/L in the other unit.
How to read your score
Frequently asked questions
What is the molar mass of glucose (C6H12O6)?
It is 180.156 g/mol. That is the sum of the standard atomic weights of every atom in the formula: 6 × 12.011 (C) + 12 × 1.008 (H) + 6 × 15.999 (O). One mole of glucose therefore weighs 180.156 g, and a gram of it is 5.5507 mmol.
What percentage of glucose is oxygen?
53.28% by mass. Each formula unit contains 6 oxygen atoms contributing 95.994 g of the 180.156 g total, so 100 g of glucose contains 53.28 g of oxygen and a kilogram contains 532.84 g of it.
How do I convert blood glucose from mg/dL to mmol/L?
Multiply by 10 and divide by the molar mass, 180.156 g/mol — a single factor of 0.0555074 for glucose. To go back the other way, multiply the mmol/L figure by 18.0156.
What is the reference range for blood glucose in both units?
Taking 70–100 mg/dL as the interval (fasting), that is 3.886–5.551 mmol/L. Every laboratory publishes its own interval and the one printed on the report is the one that applies.
Why can I not use one conversion factor for the whole report?
Because the factor is the molar mass, and that differs for every analyte. For glucose it is 0.0555074; a factor borrowed from another test gives a result that looks reasonable and is wrong by whatever ratio separates the two molar masses.
What about mg/L and µmol/L?
A decilitre is 100 mL, so mg/dL × 10 is mg/L: 70 mg/dL is 700 mg/L. Micromoles are millimoles × 1000, so the same result is 3885.5 µmol/L. Reports for trace analytes use µmol/L to avoid decimals.
Unit conversion table for glucose
| Element | Atoms | Atomic weight | Contribution (g/mol) | By mass |
|---|---|---|---|---|
| Oxygen (O) | 6 | 15.999 | 95.994 | 53.28% |
| Carbon (C) | 6 | 12.011 | 72.066 | 40% |
| Hydrogen (H) | 12 | 1.008 | 12.096 | 6.714% |
| Total — one mole of glucose | 180.156 | 100% |
Standard atomic weights, IUPAC 2021. The contribution column is atoms × atomic weight, and the total is the molar mass this page uses: 180.156 g/mol.
| mg/dL | mmol/L | µmol/L | mg/L | Against reference |
|---|---|---|---|---|
| 35 mg/dL | 1.9428 | 1942.8 | 350 | below range |
| 44.615 mg/dL | 2.4765 | 2476.5 | 446.15 | below range |
| 54.231 mg/dL | 3.0102 | 3010.2 | 542.31 | below range |
| 63.846 mg/dL | 3.5439 | 3543.9 | 638.46 | below range |
| 73.462 mg/dL | 4.0777 | 4077.7 | 734.62 | within range |
| 83.077 mg/dL | 4.6114 | 4611.4 | 830.77 | within range |
| 92.692 mg/dL | 5.1451 | 5145.1 | 926.92 | within range |
| 102.31 mg/dL | 5.6788 | 5678.8 | 1023.1 | above range |
| 111.92 mg/dL | 6.2126 | 6212.6 | 1119.2 | above range |
| 121.54 mg/dL | 6.7463 | 6746.3 | 1215.4 | above range |
| 131.15 mg/dL | 7.28 | 7280 | 1311.5 | above range |
| 140.77 mg/dL | 7.8137 | 7813.7 | 1407.7 | above range |
| 150.38 mg/dL | 8.3475 | 8347.5 | 1503.8 | above range |
| 160 mg/dL | 8.8812 | 8881.2 | 1600 | above range |
Conversion factor mg/dL × 10 ÷ 180.156 = mmol/L. Reference interval taken as 70–100 mg/dL (fasting); laboratories publish their own intervals and those are the ones that apply to a result.
| Compound | Formula | Molar mass (g/mol) | Millimoles in 1 g |
|---|---|---|---|
| Tris base | C4H11NO3 | 121.136 | 8.2552 |
| Paracetamol | C8H9NO2 | 151.165 | 6.6153 |
| Uric acid | C5H4N4O3 | 168.112 | 5.9484 |
| Glucose (this page) | C6H12O6 | 180.156 | 5.5507 |
| Aspirin | C9H8O4 | 180.159 | 5.5507 |
| Caffeine | C8H10N4O2 | 194.194 | 5.1495 |
| EDTA | C10H16N2O8 | 292.244 | 3.4218 |
Ordered by molar mass. The last column is 1000/M, which is the number a weighed gram actually gives you.