Guide · Published October 28, 2026 · By the site maintainer
Blood sugar units: convert mg/dL to mmol/L
Divide a mg/dL reading by 18 to get mmol/L. Multiply a mmol/L reading by 18 to get mg/dL. That single rule converts any blood glucose value between the two scales used worldwide, and it is accurate to well within the rounding your meter already applies.
The United States reports blood glucose in milligrams per deciliter (mg/dL), as do Japan and a few other countries. Most of the rest of the world — the United Kingdom, Canada, Europe, Australia — reports in millimoles per liter (mmol/L). The blood is the same and the glucose is the same; only the counting unit changes. One scale weighs the glucose in a sample, the other counts its molecules, and the molar mass of glucose is what links them.
Why the factor is 18
A mole of glucose weighs about 180 grams, so one millimole weighs about 180 milligrams. A liter holds ten deciliters, which puts a factor of 18 between a concentration expressed in mg/dL and the same concentration in mmol/L: 1 mmol/L = 18 mg/dL. The clinically exact factor, from the precise molar mass of glucose (180.156 g/mol), is 18.016 — labs use a multiplier of 0.0555 going from mg/dL to mmol/L. The difference between dividing by 18 and dividing by 18.016 is a fraction of a percent, invisible on a home meter that rounds to the nearest whole mg/dL or tenth of a mmol/L.
Conversion table
| mg/dL | mmol/L |
|---|---|
| 54 mg/dL | 3.0 mmol/L |
| 70 mg/dL | 3.9 mmol/L |
| 80 mg/dL | 4.4 mmol/L |
| 90 mg/dL | 5.0 mmol/L |
| 100 mg/dL | 5.6 mmol/L |
| 110 mg/dL | 6.1 mmol/L |
| 120 mg/dL | 6.7 mmol/L |
| 126 mg/dL | 7.0 mmol/L |
| 140 mg/dL | 7.8 mmol/L |
| 160 mg/dL | 8.9 mmol/L |
| 180 mg/dL | 10.0 mmol/L |
| 200 mg/dL | 11.1 mmol/L |
| 250 mg/dL | 13.9 mmol/L |
| 300 mg/dL | 16.7 mmol/L |
Two anchors make most readings easy to place without a table: 100 mg/dL is 5.6 mmol/L, and 180 mg/dL is exactly 10.0 mmol/L. From those, every 18 mg/dL step is one mmol/L step, so a reading of 144 is 8.0 and a reading of 216 is 12.0.
The reference points in both units
Certain readings carry standard clinical meanings, and travelers meet them in whichever unit the local system uses. Below 70 mg/dL (3.9 mmol/L) is the widely used alert threshold for low blood sugar. A normal fasting range for people without diabetes is roughly 70 to 99 mg/dL (3.9 to 5.5 mmol/L). A fasting reading of 126 mg/dL (7.0 mmol/L) or higher, confirmed on repeat testing, is one of the standard diagnostic criteria for diabetes, and 100 to 125 mg/dL (5.6 to 6.9 mmol/L) fasting is the range usually labeled prediabetes. Many diabetes care plans use below 180 mg/dL (10.0 mmol/L) two hours after a meal as a target. These are general reference points, not personal targets — individual goals vary and belong to a conversation with your own clinician.
Worked examples
An American meter abroad. You test in London and a borrowed meter shows 7.2 mmol/L. In the units your logbook uses: 7.2 × 18 = 130 mg/dL (129.6 before rounding).
An American reading for a European care team. Your meter at home in Ohio reads 162 mg/dL. Reported the other way: 162 ÷ 18 = 9.0 mmol/L exactly.
Reading a foreign article or forum. A British diabetes forum mentions a morning reading of 5.5. That is 5.5 × 18 = 99 mg/dL — an ordinary fasting value, not the emergency the small number might suggest to American eyes. The reverse panic happens too: 250 looks modest in mmol/L terms until it is converted to 13.9, and looks alarming as a raw number to someone expecting mg/dL. Always check the unit before reacting to the number.
Not the same as HbA1c
Hemoglobin A1c is a different measurement — a percentage (or, in much of the world, mmol/mol) reflecting average glucose over roughly three months — and it does not use the divide-by-18 rule. Converting A1c between % and mmol/mol uses its own formula: mmol/mol = 10.93 × A1c% − 23.5. So a 7.0% A1c is about 53 mmol/mol, which has nothing to do with the 7.0 mmol/L that equals 126 mg/dL on a glucose meter. The two 7.0s are a coincidence of scales and a genuine source of confusion; keep the conversions separate.
Most modern meters can switch their display unit in settings, which is the safest fix when you move between systems — a converted reading is only as good as the arithmetic, and a meter that natively shows the unit your care team uses removes the risk entirely. For other everyday unit pairs, see the full conversion chart. This guide is general information about units, not medical advice.