Blood Sugar Converter: mg/dL to mmol/L
Enter a blood glucose reading and this converter instantly switches it between mg/dL (US, Japan) and mmol/L (UK, Canada, Australia, most of Europe). Choose fasting or post-meal context to see your ADA 2025 category - normal, prediabetes, or diabetes threshold - alongside the exact conversion formula. A full reference table with both units is shown below.
Formula
Worked example
A fasting reading of 100 mg/dL: 100 ÷ 18.0182 = 5.55 mmol/L, placing it just at the prediabetes boundary (ADA 2025: prediabetes starts at 5.6 mmol/L). In the other direction, 5.55 mmol/L x 18.0182 = 99.99 mg/dL.
Why two different units for blood sugar?
Blood glucose is measured in milligrams per deciliter (mg/dL) in the United States and Japan, and in millimoles per litre (mmol/L) in the United Kingdom, Canada, Australia, and most of Europe. Both describe the same physical quantity - the concentration of glucose in blood plasma - but use different mathematical scales. mg/dL expresses mass per volume; mmol/L expresses moles per volume. Because glucose has a molecular weight of approximately 180.16 grams per mole, dividing a mg/dL value by 18.0182 gives the exact mmol/L equivalent, and multiplying in the opposite direction converts back. The rounded factor of 18 is widely used and introduces only a tiny rounding error (less than 0.1%).
ADA 2025 diagnostic thresholds
The American Diabetes Association 2025 Standards of Care define the following fasting plasma glucose thresholds: 70-99 mg/dL (3.9-5.5 mmol/L) is normal; 100-125 mg/dL (5.6-6.9 mmol/L) is impaired fasting glucose (IFG), the fasting component of prediabetes; and 126 mg/dL (7.0 mmol/L) or above on two separate occasions meets the diagnostic criterion for diabetes. For a 75-gram oral glucose tolerance test (OGTT), a 2-hour result of 140-199 mg/dL (7.8-11.0 mmol/L) indicates impaired glucose tolerance (IGT), and 200 mg/dL (11.1 mmol/L) or above on two occasions indicates diabetes. HbA1c of 5.7-6.4% is the prediabetes range; 6.5% or above is the diabetes threshold. A single abnormal result is not sufficient for a diagnosis except when classic hyperglycemia symptoms are present.
Hypoglycemia: when glucose goes too low
Hypoglycemia is defined as blood glucose below 70 mg/dL (3.9 mmol/L). Levels between 54 and 69 mg/dL (3.0-3.8 mmol/L) generally require prompt action such as consuming fast-acting carbohydrates (glucose tablets, juice, or regular soft drink). Levels below 54 mg/dL (3.0 mmol/L) are classified as severe hypoglycemia and constitute a medical emergency, particularly in people on insulin or certain diabetes medications. Symptoms include shakiness, sweating, confusion, and in severe cases loss of consciousness. People with diabetes should follow their individualised care plan for managing low readings.
Reading your glucometer abroad
Travelers and international patients frequently need to interpret glucose readings measured on a device calibrated for a different country. If you normally use a US glucometer (mg/dL) and are seeing a European lab result in mmol/L, simply multiply the mmol/L figure by 18 to get the rough mg/dL equivalent. In the other direction, divide mg/dL by 18. For example, a reading of 7.5 mmol/L shown on a UK device equals approximately 135 mg/dL. Many modern glucometers allow you to switch between unit systems in their settings menu; check your device manual if you need to change the displayed unit rather than just converting the number.
Blood glucose reference ranges: mg/dL and mmol/L
| Category | Fasting mg/dL | Fasting mmol/L | Status |
|---|---|---|---|
| Severe hypoglycemia | Below 54 | Below 3.0 | Medical emergency |
| Hypoglycemia | 54-69 | 3.0-3.8 | Low |
| Normal | 70-99 | 3.9-5.5 | Healthy |
| Prediabetes (IFG) | 100-125 | 5.6-6.9 | Elevated |
| Diabetes threshold | 126 or above | 7.0 or above | Diagnostic level |
| High | 180-249 | 10.0-13.8 | Requires attention |
| Very high | 250 or above | 13.9 or above | Seek prompt care |
Fasting thresholds per ADA Standards of Care 2025. Post-meal (2-hour) normal is below 140 mg/dL (7.8 mmol/L); prediabetes is 140-199 mg/dL (7.8-11.0 mmol/L); diabetes threshold is 200 mg/dL (11.1 mmol/L) or above.
Frequently asked questions
What is the exact conversion factor between mg/dL and mmol/L?
The exact factor is 18.0182, derived from glucose's molecular weight of 180.16 g/mol divided by 10 (to account for the dL-to-L difference). In practice, dividing by 18 or multiplying by 18 is accurate enough for clinical use, introducing less than 0.1% error. This calculator uses the precise 18.0182 factor.
What is a normal fasting blood sugar level?
The ADA 2025 Standards of Care define a normal fasting plasma glucose as 70-99 mg/dL (3.9-5.5 mmol/L) after at least 8 hours without food. A reading of 100-125 mg/dL (5.6-6.9 mmol/L) falls in the prediabetes range, and 126 mg/dL (7.0 mmol/L) or above on two occasions meets the diabetes diagnostic threshold.
What is a normal blood sugar after eating?
For people without diabetes, a 2-hour post-meal blood glucose below 140 mg/dL (7.8 mmol/L) is considered normal. Levels of 140-199 mg/dL (7.8-11.0 mmol/L) at the 2-hour mark indicate impaired glucose tolerance (IGT), the post-meal component of prediabetes. A 2-hour result of 200 mg/dL (11.1 mmol/L) or above on two occasions meets the ADA diagnostic criterion for diabetes.
Why does the US use mg/dL while most other countries use mmol/L?
The difference is historical. The US adopted the metric weight-per-volume convention (mg/dL) in the early twentieth century and has not switched to the molar concentration system (mmol/L) that most countries standardised on after the Systeme International d'Unites was adopted. Both units are scientifically valid; the difference is purely one of convention and creates no clinical risk as long as the correct unit is identified.
Can I convert a 5.6 mmol/L reading to mg/dL?
5.6 mmol/L x 18.0182 = approximately 100.9 mg/dL. This places the reading right at the ADA prediabetes boundary for fasting glucose (100-125 mg/dL or 5.6-6.9 mmol/L).
What is a dangerous blood sugar level?
Below 54 mg/dL (3.0 mmol/L) is severe hypoglycemia and a medical emergency. Above 250 mg/dL (13.9 mmol/L) is very high and warrants prompt medical attention; very high levels can indicate diabetic ketoacidosis or hyperosmolar hyperglycemic state. Always follow your doctor's guidance and call emergency services if you or someone else loses consciousness.
What does HbA1c measure and how does it relate to blood glucose?
HbA1c (glycated haemoglobin) reflects average blood glucose over the preceding 2-3 months, expressed as a percentage of haemoglobin that has glucose attached. The ADA 2025 criteria define normal HbA1c as below 5.7%, prediabetes as 5.7-6.4%, and diabetes as 6.5% or above. An HbA1c of 6.5% roughly corresponds to an average glucose of about 140 mg/dL (7.8 mmol/L). Unlike single glucose readings, HbA1c is not affected by short-term dietary or activity changes.