Blood Sugar Calculator

The US uses mg/dL (mass concentration) while most other countries use mmol/L (molar concentration). Both measure exactly the same thing — the glucose concentration in your blood — just in different units.

Doctors and researchers in the US grew up with mg/dL because it pairs naturally with the imperial measurement system used in lab reporting. The rest of the world standardized on SI units (moles per liter) decades ago.

This calculator handles both directions instantly so a US patient can read a European lab report and vice versa.

ADA cutoffs divide blood sugar into normal, prediabetes, and diabetes ranges, but the underlying biology is a spectrum. Glucose creeps up gradually over years before crossing into diagnostic range, and the longer it sits in the prediabetes zone, the higher the risk of progression.

Many people only learn they have prediabetes from a routine annual physical.

If your reading falls into the borderline range, that's not a diagnosis — it's an early warning that diet, exercise, and weight management can still reverse the trajectory.

According to the American Diabetes Association:

• a normal fasting blood glucose is below 100 mg/dL (5.6 mmol/L)
• a normal reading two hours after eating is below 140 mg/dL (7.8 mmol/L)
• For the A1C test, which reflects average glucose over 2-3 months, below 5.7% is normal

These thresholds are the basis for the categories this calculator reports, but only a healthcare provider can diagnose diabetes using repeat testing.

Blood sugar is measured in mg/dL in the US and mmol/L in most of the world.

To convert, divide mg/dL by 18 to get mmol/L, or multiply mmol/L by 18 to get mg/dL. For example, 100 mg/dL equals about 5.6 mmol/L, and 7 mmol/L equals about 126 mg/dL.

This calculator shows both units automatically so readings can be compared across countries and devices without manual math.

The A1C (HbA1c) test measures the percentage of hemoglobin coated with sugar, reflecting average blood glucose over roughly three months rather than a single moment.

Per the NIH's NIDDK, an A1C of 5.7-6.4% indicates prediabetes and 6.5% or higher indicates diabetes.

A1C correlates with an estimated average glucose, which this calculator provides. Because it averages, A1C can miss short-term highs and lows that daily testing catches.

The ADA defines clear diagnostic ranges:

• Fasting glucose of 100-125 mg/dL is prediabetes and 126 mg/dL or higher (on repeat testing) is diabetes
• A two-hour post-meal or oral glucose tolerance value of 140-199 mg/dL is prediabetes and 200 mg/dL or higher is diabetes

Prediabetes is a warning stage where lifestyle changes can often prevent progression. Any result in these ranges should be confirmed and interpreted by a clinician.

Blood sugar below 70 mg/dL (3.9 mmol/L) is considered low (hypoglycemia) and can cause:

• shakiness
• sweating
• confusion
• rapid heartbeat
• if severe, loss of consciousness

It most often affects people with diabetes on insulin or certain medications. The ADA's '15-15 rule' — consume 15 grams of fast carbs, wait 15 minutes, recheck — is the standard first response.

Frequent or severe lows need medical review of medication and diet.

Many things move blood glucose:

• carbohydrate intake
• portion size
• physical activity (which lowers it)
• illness and infection
• stress hormones
• sleep
• dehydration
• certain medications
• for people with diabetes, insulin timing

This is why a single reading is a snapshot, not the whole picture.

Understanding your personal patterns — how meals, exercise, hydration, and stress shift your numbers — is central to interpreting readings and, for those with diabetes, to management; because dehydration concentrates blood glucose, keeping fluids steady with a water intake calculator is a simple lever many people overlook.

For many non-pregnant adults with diabetes, the ADA suggests target ranges of roughly 80-130 mg/dL before meals and under 180 mg/dL two hours after, with an A1C goal often below 7% — though targets are individualized by age, health, and risk of hypoglycemia.

Tighter or looser goals may be appropriate for some.

These are management targets set with a care team, not diagnostic cutoffs, and should be personalized by a clinician.

Evidence-based ways to improve blood sugar include:

• a balanced diet emphasizing fiber and limiting refined carbs and sugary drinks
• regular physical activity
• weight management
• adequate sleep
• stress reduction
• when prescribed, medication taken as directed

The CDC's National Diabetes Prevention Program shows structured lifestyle change can substantially cut the risk of progressing from prediabetes to diabetes. Any medication or major dietary change should be guided by a healthcare professional.

Errors that distort readings include:

• testing without washing hands (food residue raises results)
• using expired or improperly stored strips
• dehydration
• testing at inconsistent times relative to meals
• comparing fasting to post-meal values as if equivalent

People also over-interpret a single reading.

Test at consistent times, follow device instructions, log results with context (meals, activity), and share trends with your provider rather than reacting to one isolated number.