Reading your own glucose numbers can be confusing when one clinic prints mg/dL and another prints mmol/L. A result of "5.6" sounds nothing like "100" even though they describe the exact same blood sugar. This glucose conversion calculator does one job and does it cleanly: it translates between the two units the world uses to report blood glucose, and it converts an HbA1c percentage into the estimated average glucose (eAG) that percentage represents — in both units at once.
Type a number, pick the unit it is in, and the other unit appears instantly. Whether you are comparing an old lab report to a new continuous-glucose-monitor readout, reading a prescription from a country that uses mmol/L, or explaining a child's glucose log to a grandparent, this tool removes the mental math so you never have to guess whether "9" is dangerously high or perfectly normal.
How to Use
- Enter the Glucose Value — the number printed on your meter, CGM, or lab slip.
- Set the Reading Unit to match that number. Choose mg/dL if the meter is a US device, or mmol/L if it was sold in Europe, Asia, Australia, or most of the rest of the world. The result card immediately shows the same value converted into the other unit.
- Optionally enter your HbA1c as a percentage (for example
5.7). The tool then reports the estimated average glucose (eAG) that this HbA1c corresponds to, shown in both mg/dL and mmol/L. - Read the highlighted result: your glucose in the other unit, plus the HbA1c your single reading would roughly average out to.
The engine multiplies or divides by 18.0182 — the standard conversion factor derived from the molar mass of glucose (180.156 g/mol, divided by 10). For a quick mental check, people often round it to 18: divide mg/dL by 18, or multiply mmol/L by 18. That shortcut is accurate enough for everyday reading, and the calculator gives you the precise figure.
The Conversion Factor: Why 18?
Blood glucose measures concentration. In the United States it is reported in milligrams per deciliter (mg/dL) — how many milligrams of glucose sit in 0.1 liters of blood. Nearly everywhere else it is reported in millimoles per liter (mmol/L) — how many 180-milligram molecules of glucose sit in one liter.
Because one mole of glucose weighs about 180 grams, and a deciliter is one-tenth of a liter, the two scales are linked by a constant of roughly 18:
- mg/dL → mmol/L: divide by 18.0182
- mmol/L → mg/dL: multiply by 18.0182
So 100 mg/dL ≈ 5.6 mmol/L, and 9 mmol/L ≈ 162 mg/dL. The two numbers never mean different things — they are just two rulers marked in different units.
HbA1c and Estimated Average Glucose (eAG)
A fingerstick tells you your sugar at one instant. An HbA1c test reflects your average blood sugar over roughly the past three months. Because the percentage is hard for patients to picture, the American Diabetes Association popularized eAG — estimated average glucose — which converts HbA1c back into the mg/dL (or mmol/L) number people recognize.
The regression is:
eAG (mg/dL) = 28.7 × HbA1c% − 46.7
For example, an HbA1c of 5.7% gives an eAG of about 117 mg/dL, or roughly 6.5 mmol/L. A result of 7.0% corresponds to an average of about 154 mg/dL (8.5 mmol/L). Entering your HbA1c in the optional field shows you this average in both units, so you can compare it directly against your day-to-day readings.
Examples
Example 1 — The classic conversion. A US meter reads 100 mg/dL. Switch the Reading Unit to mg/dL and enter 100. The result card shows 100 mg/dL = 5.6 mmol/L. A friend in London whose meter says 5.6 is at exactly the same blood sugar — the units, not the health, differ.
Example 2 — Reading a foreign lab slip. A vacation lab prints 7.8 mmol/L. You do not know whether that is high. Set Reading Unit to mmol/L and enter 7.8. The converted value is about 141 mg/dL — a typical two-hours-after-meal figure, not an emergency.
Example 3 — HbA1c to average glucose. Your annual A1c comes back at 5.7%. Enter 5.7 in the HbA1c field. The eAG shown is about 117 mg/dL (6.5 mmol/L) — the three-month average your fingersticks have been hovering around.
Example 4 — Stress-testing a large number. Entering 1,000,000 mg/dL is, of course, medically nonsensical, but the converter still handles it: it reports about 55,500 mmol/L without rounding errors, confirming the math scales correctly even for absurdly large inputs.
FAQ
How do I convert mg/dL to mmol/L?
Divide the mg/dL value by 18.0182. For example, 100 mg/dL ÷ 18.0182 ≈ 5.6 mmol/L. For a quick estimate, divide by 18. This calculator does the division for you the moment you pick the source unit.
How do I convert mmol/L back to mg/dL?
Multiply the mmol/L value by 18.0182. For example, 9 mmol/L × 18.0182 ≈ 162 mg/dL. To estimate in your head, multiply by 18.
Why do some countries use mg/dL and others use mmol/L?
It is purely a units-of-measurement convention. The United States uses mg/dL (milligrams per deciliter); almost every other country, including the United Kingdom, Canada, Australia, India, China, and the nations of the European Union, uses mmol/L (millimoles per liter). The underlying glucose concentration is identical.
What does an HbA1c of 5.7% mean in average glucose?
Using the ADA eAG formula, 5.7% corresponds to an estimated average glucose of about 117 mg/dL, or roughly 6.5 mmol/L. This is a three-month average, not a single fingerstick value.
Is 5.6 mmol/L the same as 100 mg/dL?
Yes. Converting 100 mg/dL by dividing by 18.0182 gives about 5.55 mmol/L, which rounds to the commonly cited 5.6 mmol/L. They represent the same blood glucose concentration in different units.
What is a normal blood glucose number after conversion?
Fasting readings under about 100 mg/dL (5.6 mmol/L) are typical for many adults, while readings 2 hours after a meal usually stay under 140 mg/dL (7.8 mmol/L). This tool only converts units; for diagnosis or treatment decisions, always rely on the ranges your own clinician gives you.
Disclaimer
This glucose conversion calculator is provided for informational purposes only and is not medical advice. Converted figures are estimates based on the standard 18.0182 factor and the ADA eAG regression; actual meter and lab readings may differ slightly. This tool does not diagnose diabetes, predict hypoglycemia or hyperglycemia, or replace professional medical guidance. Always confirm results and discuss treatment decisions with a qualified healthcare provider.