Blood Sugar Converter
Free Blood sugar Calculator with medically-sourced formulas. Enter your measurements for personalized, accurate health insights.
Reviewed by Rahul Singh, Health & Wellness Specialist
Formula
mmol/L = mg/dL / 18.0182 | eAG (mg/dL) = 28.7 x HbA1c - 46.7
The conversion factor 18.0182 is derived from the molecular weight of glucose (180.182 g/mol). The estimated average glucose (eAG) formula was established by the ADAG study, relating HbA1c percentage to average blood glucose over 2-3 months.
Worked Examples
Example 1: Standard Unit Conversion
Problem:A patient in the UK has a fasting blood glucose of 6.8 mmol/L. Convert to mg/dL and classify the result.
Solution:Conversion: 6.8 mmol/L x 18.0182 = 122.5 mg/dL\n\nFasting classification:\n- mg/dL: 122.5 (between 100-125) = Prediabetes range\n- mmol/L: 6.8 (between 5.6-6.9) = Prediabetes range\n\nBoth units give the same clinical interpretation. The patient has impaired fasting glucose consistent with prediabetes.
Result:6.8 mmol/L = 122.5 mg/dL | Prediabetes Range (Fasting) | Recommend OGTT for confirmation
Example 2: HbA1c to Average Glucose Conversion
Problem:A patient has an HbA1c of 7.2%. Calculate the estimated average glucose in both mg/dL and mmol/L.
Solution:Using ADAG formula: eAG (mg/dL) = 28.7 x HbA1c - 46.7\neAG = 28.7 x 7.2 - 46.7 = 206.64 - 46.7 = 159.9 mg/dL\n\nConverting to mmol/L: 159.9 / 18.0182 = 8.87 mmol/L\n\nHbA1c 7.2% classification: Diabetes (above 6.5%)\nThis means the patient average blood sugar over the past 2-3 months has been approximately 160 mg/dL.
Result:HbA1c 7.2% = eAG 159.9 mg/dL (8.87 mmol/L) | Diabetes Range | Above ADA target of < 7%
Frequently Asked Questions
What is the difference between mg/dL and mmol/L for blood sugar measurement?
Blood glucose can be measured in two different units depending on the country and laboratory system. Milligrams per deciliter (mg/dL) is the standard unit used in the United States, Japan, France, and several other countries. Millimoles per liter (mmol/L) is used in the United Kingdom, Canada, Australia, and most other countries worldwide. The conversion factor between these units is 18.0182, meaning you divide mg/dL by 18.0182 to get mmol/L, or multiply mmol/L by 18.0182 to get mg/dL. This factor is derived from the molecular weight of glucose (180.182 g/mol). Understanding both units is important for patients who travel internationally, use devices calibrated in different units, or read medical literature from different countries.
What are the normal blood sugar ranges for fasting and post-meal readings?
Normal fasting blood glucose is below 100 mg/dL (5.6 mmol/L) according to the American Diabetes Association. Fasting values between 100 and 125 mg/dL (5.6 to 6.9 mmol/L) indicate impaired fasting glucose or prediabetes, while values of 126 mg/dL (7.0 mmol/L) or higher on two separate occasions indicate diabetes. For post-meal readings (measured 2 hours after eating), normal is below 140 mg/dL (7.8 mmol/L), prediabetes ranges from 140 to 199 mg/dL (7.8 to 11.0 mmol/L), and diabetes is 200 mg/dL (11.1 mmol/L) or higher. Random blood glucose of 200 mg/dL or higher with symptoms of hyperglycemia also meets diagnostic criteria for diabetes. These thresholds are based on large population studies correlating glucose levels with risk of diabetic complications.
How does HbA1c relate to average blood sugar levels?
Hemoglobin A1c (HbA1c or glycated hemoglobin) reflects average blood glucose over the preceding 2 to 3 months by measuring the percentage of hemoglobin proteins that have glucose attached to them. The A1c-Derived Average Glucose (ADAG) study established the relationship between HbA1c and estimated average glucose using the formula: eAG (mg/dL) = 28.7 x HbA1c - 46.7. For example, an HbA1c of 6.0% corresponds to an average glucose of about 126 mg/dL (7.0 mmol/L), while an HbA1c of 7.0% corresponds to about 154 mg/dL (8.6 mmol/L). Normal HbA1c is below 5.7%, prediabetes is 5.7% to 6.4%, and diabetes is 6.5% or higher. HbA1c is particularly valuable because it is not affected by short-term fluctuations and does not require fasting for the blood draw.
Why do blood sugar readings vary throughout the day and what factors affect them?
Blood glucose levels naturally fluctuate throughout the day in response to numerous physiological and behavioral factors. The most obvious influence is food intake, as carbohydrates are broken down into glucose during digestion, causing blood sugar to rise within 15 to 30 minutes of eating and typically peaking at 1 to 2 hours. Physical activity lowers blood sugar by increasing glucose uptake into muscle cells. Stress hormones like cortisol and adrenaline raise blood sugar through glycogenolysis and gluconeogenesis. The dawn phenomenon causes blood sugar to rise in the early morning hours due to growth hormone and cortisol secretion. Medications, illness, sleep quality, dehydration, and alcohol consumption all influence glucose levels. For people with diabetes, insulin timing, dosage, and injection site absorption can cause additional variability in readings.
References
Reviewed by Rahul Singh, Health & Wellness Specialist · Editorial policy