Blood Sugar Converter: mg/dL ↔ mmol/L Glucose Unit Guide
Whether you just got a lab report from a US clinic while living in the UK, you're reading an international diabetes study, or you're comparing your glucose monitor's reading with your doctor's notes — blood sugar unit confusion is one of the most common frustrations in diabetes management. This guide explains everything you need to know about converting blood glucose values between mg/dL and mmol/L, including the formula, normal ranges, country-by-country standards, and how to interpret your readings correctly.
What Units Are Used to Measure Blood Sugar?
There are two standard units used worldwide to express blood glucose (blood sugar) levels:
mg/dL — Milligrams per Deciliter
mg/dL measures the weight of glucose (in milligrams) dissolved in one deciliter of blood. It is the older of the two standards and remains dominant in countries such as the United States, Japan, South Korea, Egypt, and Israel. If your glucometer displays numbers like 90, 120, or 180, it is reading in mg/dL.
mmol/L — Millimoles per Liter
mmol/L measures the molar concentration of glucose — the number of molecules of glucose per liter of blood. This is the SI (International System of Units) standard, adopted by the United Kingdom, Canada, Australia, New Zealand, and most of Europe and Asia. If your device shows numbers like 5.0, 6.6, or 10.0, it is reading in mmol/L.
The two scales express the exact same physical quantity — the concentration of glucose in your blood — using different mathematical frameworks. Neither is more accurate than the other; they are simply different languages for the same measurement.
How to Convert Blood Sugar: The Formula
The relationship between mg/dL and mmol/L is fixed and simple. Glucose has a molecular weight of 180.16 g/mol, which gives us the conversion factor of 18.
mg/dL → mmol/L
mmol/L = mg/dL ÷ 18
Example: 126 mg/dL ÷ 18 = 7.0 mmol/L
mmol/L → mg/dL
mg/dL = mmol/L × 18
Example: 7.8 mmol/L × 18 = 140 mg/dL
Quick Reference: Common Conversion Values
| mg/dL |
mmol/L |
Clinical Context |
| 54 | 3.0 | Severe hypoglycemia |
| 70 | 3.9 | Lower limit of normal (fasting) |
| 90 | 5.0 | Ideal fasting level |
| 100 | 5.6 | Top of normal fasting range |
| 108 | 6.0 | Early prediabetes signal |
| 126 | 7.0 | Diabetes threshold (fasting) |
| 140 | 7.8 | Normal 2-hour post-meal ceiling |
| 154 | 8.6 | — |
| 180 | 10.0 | Post-meal caution threshold |
| 200 | 11.1 | Diabetes threshold (post-meal/random) |
| 270 | 15.0 | High — seek medical advice |
| 360 | 20.0 | Very high — urgent attention |
💡 Tip for mental math: Divide mg/dL by 18 (or roughly by 20 for a quick estimate). Multiply mmol/L by 18 to go the other direction.
Normal Blood Sugar Ranges: mg/dL and mmol/L Side by Side
Understanding your number requires knowing the reference range. These are the widely accepted standards from the American Diabetes Association (ADA) and Diabetes UK:
Fasting Blood Glucose (no food for 8+ hours)
| Status | mg/dL | mmol/L |
|---|
| Normal | 70 – 99 | 3.9 – 5.5 |
| Prediabetes | 100 – 125 | 5.6 – 6.9 |
| Diabetes | 126 or above | 7.0 or above |
2-Hour Post-Meal (Postprandial) Blood Glucose
| Status | mg/dL | mmol/L |
|---|
| Normal | Less than 140 | Less than 7.8 |
| Prediabetes | 140 – 199 | 7.8 – 11.0 |
| Diabetes | 200 or above | 11.1 or above |
Random Blood Glucose (any time of day)
| Status | mg/dL | mmol/L |
|---|
| Normal | 70 – 140 | 3.9 – 7.8 |
| Concern | 140 – 199 | 7.8 – 11.0 |
| Diabetes (with symptoms) | 200 or above | 11.1 or above |
Target Ranges for People Already Diagnosed with Diabetes
These targets vary by individual and should be agreed with your doctor, but common guidance from the ADA includes:
- Before meals: 80–130 mg/dL (4.4–7.2 mmol/L)
- 1–2 hours after meals: Less than 180 mg/dL (less than 10.0 mmol/L)
- Bedtime: 100–140 mg/dL (5.6–7.8 mmol/L)
Which Countries Use mg/dL vs mmol/L?
This question drives a lot of the search traffic around "blood glucose conversion" — particularly when people travel, consult international doctors, or read studies from another country.
Countries Using mg/dL
- 🇺🇸 United States
- 🇯🇵 Japan
- 🇰🇷 South Korea
- 🇪🇬 Egypt
- 🇮🇱 Israel
- 🇧🇷 Brazil (some labs use both)
Countries Using mmol/L
- 🇬🇧 United Kingdom
- 🇨🇦 Canada
- 🇦🇺 Australia
- 🇳🇿 New Zealand
- 🇩🇪 Germany & 🇫🇷 France
- 🇸🇪 Sweden & 🇳🇱 Netherlands
- 🇨🇳 China & 🇮🇳 India
- 🇿🇦 South Africa
- Most of Europe, Africa & Asia
If you're a British patient reading an American medical study, or an Australian seeing a doctor in Japan, this converter bridges that gap.
HbA1c vs Blood Glucose: Understanding the Difference
You may also see HbA1c (glycated haemoglobin) on lab reports. This is not the same as a blood glucose reading, so you cannot use the mg/dL ↔ mmol/L formula here.
HbA1c reflects your average blood sugar over the past 2–3 months and is expressed as a percentage (%) or — increasingly in Europe — as mmol/mol (a completely different mmol unit from blood glucose).
| HbA1c % |
HbA1c mmol/mol |
Avg Glucose (mg/dL) |
Avg Glucose (mmol/L) |
| 5.0% | 31 | 97 | 5.4 |
| 5.7% | 39 | 117 | 6.5 |
| 6.0% | 42 | 126 | 7.0 |
| 6.5% | 48 | 140 | 7.8 |
| 7.0% | 53 | 154 | 8.6 |
| 8.0% | 64 | 183 | 10.2 |
| 9.0% | 75 | 212 | 11.8 |
| 10.0% | 86 | 240 | 13.4 |
For HbA1c-specific conversions, see our HbA1c Calculator.
Why Do Blood Sugar Units Differ Between Countries?
The split between mg/dL and mmol/L is largely historical. The United States standardized on mg/dL decades before the global adoption of SI units — and healthcare systems don't change measurement standards easily, given the scale of lab equipment, medical records, and clinical training involved.
The International Federation of Clinical Chemistry (IFCC) and the World Health Organisation (WHO) have recommended mmol/L as the preferred unit for decades, which is why most countries that modernised their medical systems after the 1970s adopted it. The US, Japan, and a handful of others retained mg/dL due to entrenched infrastructure and the enormous cost of switching.
There is ongoing discussion in the diabetes community about global harmonisation, but for now, both systems remain in active clinical use.
Reading Your Glucometer: What Unit Is It Using?
Most modern glucometers can be switched between mg/dL and mmol/L in their settings. Here's how to tell which unit yours is displaying:
- Numbers 70–400+ — you are reading in mg/dL
- Numbers 3.9–22.2 (typically displayed with one decimal place) — you are reading in mmol/L
⚠️ Important: A reading of "5.6" is a normal fasting result in mmol/L; a reading of "56" without a decimal would be dangerously low in mg/dL (hypoglycemia). The decimal point is critical. Always confirm which unit your device is set to, especially if you've recently traveled or borrowed someone else's meter.
Hypoglycemia and Hyperglycemia: Recognising the Thresholds
Understanding your number means knowing when it signals a problem:
🔵 Hypoglycemia (Low Blood Sugar)
- Below 70 mg/dL (3.9 mmol/L): Mild — shakiness, sweating, lightheadedness
- Below 54 mg/dL (3.0 mmol/L): Clinically significant — requires immediate action
- Below 40 mg/dL (2.2 mmol/L): Severe — medical emergency
🔴 Hyperglycemia (High Blood Sugar)
- 180 mg/dL (10.0 mmol/L) after meals: Monitor closely
- Above 240 mg/dL (13.3 mmol/L): Risk of ketones (Type 1)
- Above 300 mg/dL (16.7 mmol/L): Seek urgent medical review
- Above 600 mg/dL (33.3 mmol/L): Medical emergency
These thresholds apply to people with known diabetes. If you don't have a diagnosis and are getting readings in these ranges, contact your healthcare provider promptly.
Practical Conversion Examples
Here are some real-world scenarios where the blood glucose conversion calculator is most useful:
📋 Scenario 1: Reading a US diabetes study while in the UK
The study reports a fasting threshold of 126 mg/dL. Divide by 18 → 7.0 mmol/L — exactly what your UK doctor refers to.
📱 Scenario 2: Your CGM switched units accidentally
Your monitor shows 14.4 instead of the expected ~260. Multiply 14.4 × 18 = 259.2 mg/dL — a high but not unexpected reading. The device was set to mmol/L.
🗂️ Scenario 3: Comparing a Japanese lab report
Your Tokyo report shows 108 mg/dL fasting. Divide by 18 = 6.0 mmol/L — prediabetes territory in both systems.
🇬🇧 Scenario 4: Tracking a post-meal reading on a UK meter
Your meter reads 9.2 mmol/L, two hours after eating. Multiply by 18 = 165.6 mg/dL — above the 140 mg/dL / 7.8 mmol/L normal ceiling, worth discussing with your doctor.
Frequently Asked Questions
How accurate is the blood sugar conversion?
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The conversion factor of 18 (technically 18.016, based on glucose's molecular weight) is a fixed constant. Our calculator uses the precise value, so conversions are as accurate as the measurement itself. Glucose readings always carry a small margin of error from the measuring device (typically ±10–15% for consumer glucometers under ISO 15197:2013), but the unit conversion itself introduces no additional error.
Can I use mg/dL ÷ 18 as a mental shortcut?
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Yes. Dividing by 18 gives you mmol/L accurately. For rough mental math, dividing by 20 is even faster and gives a close approximation — useful for checking whether a reading is in the right ballpark. Example: 180 mg/dL ÷ 20 = 9, which is close to the actual 10.0 mmol/L.
My glucometer shows mmol/L but my doctor uses mg/dL — can I change my device's unit?
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Most glucometers allow you to switch units in settings. Check your device manual under "units" or "settings." You can also simply use this converter to translate your readings for your appointments.
What's a normal blood sugar level for a non-diabetic person?
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For someone without diabetes: fasting should be below 100 mg/dL (5.6 mmol/L), and two hours after eating should be below 140 mg/dL (7.8 mmol/L). Single readings outside these ranges aren't diagnostic on their own — context, repeated testing, and HbA1c results give the full picture.
What's the difference between blood sugar and blood glucose?
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The terms are interchangeable in everyday clinical use. Blood glucose is technically more precise (it specifically means glucose, not other sugars), but "blood sugar" is universally understood to mean blood glucose in a medical context.
Is this tool a substitute for medical advice?
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No. This calculator helps you understand and translate your measurements accurately, but it does not interpret your health status. Always work with your doctor or certified diabetes care and education specialist (CDCES) to understand what your readings mean for you personally.
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Medical Disclaimer: This content is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of your physician or other qualified health professional with any questions you may have regarding a medical condition.