Blood glucose mg/dL to mmol/L Converter

Blood sugar in two units: the short answer

To convert blood sugar from mg/dL to mmol/L, divide by 18 (more precisely 18.016). To go from mmol/L back to mg/dL, multiply by 18. A fasting reading of 100 mg/dL is therefore 5.6 mmol/L, and a reading of 7.0 mmol/L is 126 mg/dL. The converter above does the arithmetic for you in both directions and shows where your number sits against the diagnostic thresholds used by the American Diabetes Association (ADA).

That one-line rule hides a few details that matter in practice: why the factor is 18, when the result should be rounded, whether a meter, a CGM and a laboratory are measuring the same thing, and how the familiar cut-offs translate between the two systems. This guide covers each of them, with worked examples and a full chart.

What a blood glucose test measures

Glucose is the main sugar in the blood and the primary fuel for the brain and muscles. After a meal, carbohydrates are digested into glucose, which enters the bloodstream; insulin from the pancreas then moves it into cells. Between meals the liver releases stored glucose to keep levels steady. A blood glucose test captures the concentration at a single moment, which is why the timing of the sample matters so much.

The main types of glucose measurement are:

• Fasting plasma glucose (FPG) – taken after at least 8 hours without calories. It is one of the standard tests for diagnosing diabetes and prediabetes.
• Random (casual) glucose – taken at any time regardless of meals. It is mainly useful when it is very high and symptoms are present.
• Oral glucose tolerance test (OGTT) – glucose is measured fasting and again 2 hours after drinking 75 g of glucose. It is the most sensitive test and the standard method for gestational diabetes.
• Capillary (finger-prick) glucose – measured with a home meter on a drop of whole blood. Modern meters are calibrated to report a plasma-equivalent value.
• Interstitial glucose – measured by continuous glucose monitors (CGMs) in the fluid between cells, typically every 1–5 minutes. It lags blood glucose by several minutes when levels are changing fast.

All of these report the same quantity – the concentration of glucose – and all can be shown in either unit.

mg/dL and mmol/L explained

mg/dL (milligrams per deciliter) is a mass concentration: how many milligrams of glucose are dissolved in one tenth of a liter of plasma. It is used in the United States and in some countries in Latin America, the Middle East and Asia.

mmol/L (millimoles per liter) is a molar concentration: how many millimoles of glucose molecules are present in one liter. It is the International System of Units (SI) standard and is used in the UK, Ireland, Canada, Australia, New Zealand, most of Europe, China and many other countries.

Neither unit is more accurate than the other. They are two ways of describing exactly the same amount of glucose, in the way that a distance can be written in miles or kilometers. Most meters, CGMs and diabetes apps let you choose the unit in their settings, and a meter bought in one country may arrive pre-set to that country's unit.

Why the factor is 18

The conversion comes from the molar mass of glucose (C₆H₁₂O₆), which is 180.16 grams per mole. One millimole of glucose therefore weighs 180.16 mg. A concentration of 1 mmol/L means 180.16 mg in a liter, which is 18.016 mg in a deciliter (a tenth of a liter). So:

• mmol/L = mg/dL ÷ 18.016 (equivalently mg/dL × 0.0555)
• mg/dL = mmol/L × 18.016

Most clinicians and textbooks round the factor to 18. The difference between 18 and 18.016 is less than 0.1%, which never changes a clinical category: 126 mg/dL is 7.0 mmol/L with either factor.

How to convert blood sugar step by step

1. Check the unit printed next to your result. Lab reports always state it; on a meter it appears beside the number.
2. To convert mg/dL to mmol/L, divide by 18. Round to one decimal place, which is how mmol/L results are normally shown.
3. To convert mmol/L to mg/dL, multiply by 18. Round to a whole number, which is how mg/dL results are normally shown.
4. Compare the converted value with the threshold in the same unit – for example the ADA fasting cut-off of 126 mg/dL equals 7.0 mmol/L.

Worked examples

• Fasting 92 mg/dL: 92 ÷ 18.016 = 5.11 → 5.1 mmol/L (normal fasting range).
• Fasting 112 mg/dL: 112 ÷ 18.016 = 6.22 → 6.2 mmol/L (prediabetes range, 5.6–6.9 mmol/L).
• After a meal, 9.4 mmol/L: 9.4 × 18.016 = 169.4 → 169 mg/dL.
• Hypoglycemia alert at 3.9 mmol/L: 3.9 × 18.016 = 70.3 → 70 mg/dL, the standard level 1 hypoglycemia threshold.
• CGM average of 8.6 mmol/L: 8.6 × 18.016 = 154.9 → 155 mg/dL, which corresponds to an A1C of about 7%.

Mental shortcuts

For a quick estimate without a calculator, divide mg/dL by 2, then divide by 10, then add 10% of that result: 140 → 70 → 7.0 → 7.0 + 0.7 = 7.7 mmol/L (exact answer 7.8). Going the other way, multiply mmol/L by 20 and subtract 10%: 6 × 20 = 120, minus 12 = 108 mg/dL (exact answer 108).

Blood sugar conversion chart

The tables below cover the values people most often need – from hypoglycemia thresholds to very high readings. The left table converts mg/dL to mmol/L, and the right table converts common mmol/L values back to mg/dL.

Normal blood sugar ranges and diagnostic cut-offs

The categories below are used by the ADA and match those of the World Health Organization for fasting glucose, with one difference: the WHO and many UK sources start "impaired fasting glucose" at 6.1 mmol/L (110 mg/dL), while the ADA uses 5.6 mmol/L (100 mg/dL).

A diagnosis of diabetes normally needs two abnormal results – either two different tests from the same sample or the same test repeated on another day – unless there are unmistakable symptoms with a random glucose of 200 mg/dL (11.1 mmol/L) or more.

Targets for people with diabetes

For many non-pregnant adults with diabetes, the ADA suggests a pre-meal capillary glucose of 80–130 mg/dL (4.4–7.2 mmol/L) and a peak after meals below 180 mg/dL (10.0 mmol/L). For CGM users, a widely used international consensus recommends spending more than 70% of the day between 70 and 180 mg/dL (3.9–10.0 mmol/L), with less than 4% of readings below 70 mg/dL (3.9 mmol/L) and less than 1% below 54 mg/dL (3.0 mmol/L). Targets are individualised: older adults, people prone to hypoglycemia and pregnant women often have different goals, so your clinician's targets come first.

Hypoglycemia levels

Gestational diabetes thresholds in both units

Pregnancy uses lower glucose thresholds, and it is one of the situations where unit mix-ups are most common because international guidance is written in mmol/L while many US lab reports use mg/dL. With the one-step 75 g OGTT recommended by the International Association of the Diabetes and Pregnancy Study Groups (IADPSG) and adopted by the ADA, gestational diabetes is diagnosed when any one of these values is met or exceeded:

Some US practices use a two-step approach instead (a 50 g screening test followed by a 100 g diagnostic test) with different thresholds, and the UK's NICE guideline uses a fasting value of 5.6 mmol/L or a 2-hour value of 7.8 mmol/L. Because these criteria differ, always check which protocol your clinic follows before comparing numbers.

Linking single readings with HbA1c

A single glucose reading is a snapshot; HbA1c reflects the average over roughly the previous two to three months. The two are connected by the ADAG equation, which converts an A1C into an estimated average glucose (eAG): an A1C of 6% corresponds to an average of about 126 mg/dL (7.0 mmol/L), 7% to about 154 mg/dL (8.6 mmol/L) and 8% to about 183 mg/dL (10.2 mmol/L). If your meter or CGM average is very different from the eAG implied by your A1C, it is worth discussing – possible reasons include testing mostly at certain times of day, anemia or other conditions that change red-blood-cell lifespan. You can explore this with our A1C to average glucose calculator and our HbA1c mmol/mol to percent converter.

Reading glucose results from another country

If you are looking at a report or a forum post from abroad, a quick rule of thumb tells you which unit is in use: fasting blood sugar values between about 3 and 30 are almost certainly mmol/L, while values between about 50 and 600 are mg/dL. A "normal" fasting glucose is roughly 4–5.5 in mmol/L and 70–99 in mg/dL. When travelling, keep your meter in the unit your care team uses and note any targets in both units, so that a temporary change of device or a hospital visit abroad does not lead to a dosing mistake. Insulin doses are never converted with the glucose factor; only the glucose numbers change.

Rounding and precision

Laboratories normally report mmol/L to one decimal place and mg/dL to whole numbers. When you convert, round in the same way – carrying extra decimals gives a false impression of precision, because the measurement itself has an analytical uncertainty of a few percent. Avoid converting back and forth repeatedly: 5.6 mmol/L becomes 100.9 mg/dL, which rounds to 101, and converting 101 back gives 5.6 again, but repeated rounding with a coarser factor can drift by a unit.

Meters, CGMs and lab tests: why numbers differ

Converting units correctly does not make two different devices agree. If your meter and a laboratory test taken at the same time disagree, the reason is usually one of these:

• Accuracy standards. The international standard for home meters (ISO 15197:2013) requires 95% of readings to be within ±15 mg/dL of the reference when glucose is below 100 mg/dL, and within ±15% at higher levels. Two accurate meters can legitimately differ by 20–30 mg/dL.
• Plasma versus whole blood. Plasma glucose is roughly 11% higher than whole-blood glucose. Almost all modern meters report plasma-equivalent values, but older devices may not.
• CGM lag. Interstitial glucose trails blood glucose by about 5–15 minutes, so after a meal or during exercise the CGM may read noticeably lower or higher than a finger-prick.
• Sample handling. In a lab tube left unprocessed, blood cells keep consuming glucose, lowering the result by around 5–7% per hour at room temperature unless a preservative tube is used.
• Site and technique. Unwashed fingers with sugar residue, squeezing hard, an expired strip or a strip exposed to humidity can all produce false readings.

What affects blood sugar results

Many everyday factors move glucose up or down, which is why one reading should never be interpreted in isolation:

• Food and drink – especially refined carbohydrates; the peak usually comes 1–2 hours after eating.
• Physical activity – exercise usually lowers glucose, although intense exercise can raise it briefly through stress hormones.
• Illness, infection and surgery – stress hormones such as cortisol and adrenaline raise glucose.
• Medicines – corticosteroids (for example prednisolone), some antipsychotics, thiazide diuretics and some HIV medicines can raise glucose; insulin and sulfonylureas can cause hypoglycemia.
• Sleep and the dawn phenomenon – a rise in hormones in the early morning can push fasting glucose up.
• Alcohol – can lower glucose for many hours, particularly in people using insulin.
• Pregnancy – thresholds for gestational diabetes are lower than outside pregnancy.

When to see a doctor

Contact a health professional if you have repeated fasting readings at or above 100 mg/dL (5.6 mmol/L), a result of 126 mg/dL (7.0 mmol/L) or more, or symptoms such as excessive thirst, frequent urination, unexplained weight loss, blurred vision or recurrent infections. Seek urgent care for a glucose above 250–300 mg/dL (14–17 mmol/L) with vomiting, abdominal pain, rapid breathing or drowsiness – these can be signs of diabetic ketoacidosis or a hyperosmolar state – and for any low reading with confusion or inability to eat or drink.