Blood sugar calculator to check glucose levels and diabetes risk based on WHO/ADA standards.
Four tabs: blood sugar check (fasting, 2-hour postprandial, HbA1c), unit conversion (mg/dL ↔ mmol/L), HbA1c target, and a complete classification reference.
Disclaimer: Not a substitute for medical diagnosis. Consult your doctor about blood sugar levels.
Calculator information
📋 How to use this calculator
- Pick a test type: fasting plasma glucose (FPG, after 8 hours of fasting), 2-hour post-prandial (2hPG), random plasma glucose (RPG), or HbA1c (3-month average).
- Enter the reading in mg/dL (the US standard) or mmol/L (international standard - use the conversion tab if needed).
- Click calculate to see the category per ADA guidelines: normal, prediabetes, or diabetes.
- For HbA1c, enter the percentage (%): normal under 5.7%, prediabetes 5.7-6.4%, diabetes 6.5% or higher.
- Use the conversion tab to switch units: mg/dL to mmol/L = value / 18.018, or HbA1c to eAG (estimated Average Glucose).
- Tip: routine screening is recommended every 3 years starting at age 35, or earlier if you have risk factors (overweight/obesity, family history of diabetes, hypertension, prior gestational diabetes).
🧮 Blood Glucose Classification and Conversion (ADA criteria)
Normal FPG: <100 mg/dL | Prediabetes FPG: 100-125 mg/dL | Diabetes FPG: >=126 mg/dL | Normal 2hPG: <140 | Prediabetes 2hPG: 140-199 | Diabetes 2hPG: >=200 | Normal HbA1c: <5.7% | Prediabetes: 5.7-6.4% | Diabetes: >=6.5% | Conversion: mmol/L = mg/dL / 18.018 | eAG = (28.7 x HbA1c%) - 46.7
- FPG = Fasting Plasma Glucose (no caloric intake for at least 8 hours)
- 2hPG = 2-hour Post-Prandial glucose (during a 75g OGTT or after a meal)
- RPG = Random Plasma Glucose (any time of day)
- HbA1c = Glycated hemoglobin (% of red blood cells with attached glucose)
- eAG = estimated Average Glucose (mg/dL) corresponding to HbA1c
- Diabetes RPG: >=200 mg/dL with classic symptoms (polyuria, polydipsia, unexplained weight loss)
A diabetes diagnosis requires two abnormal test results on separate days, or one abnormal result plus classic symptoms. HbA1c is less reliable in anemia, hemoglobinopathies, or chronic kidney disease. Use venous plasma for standardized results (not fingerstick capillary blood).
💡 Worked example: Patient with FPG of 118 mg/dL and HbA1c of 6.1%
Given:- Fasting Plasma Glucose (FPG): 118 mg/dL
- HbA1c: 6.1%
- Age: 45; BMI 28 (overweight)
Steps:- Check FPG category: 118 mg/dL falls in 100-125 - Prediabetes (Impaired Fasting Glucose)
- Check HbA1c: 6.1% falls in 5.7-6.4% - confirms Prediabetes
- Convert FPG to mmol/L: 118 / 18.018 = 6.55 mmol/L (above the 5.6 mmol/L normal cutoff)
- Compute eAG from HbA1c: (28.7 x 6.1) - 46.7 = 175.07 - 46.7 = 128.4 mg/dL (3-month average)
- Risk: without intervention, 5-10% of prediabetic patients progress to diabetes per year
Result: Prediabetes (IFG plus elevated HbA1c). eAG = 128 mg/dL. Recommendations: lose 5-7% of body weight, 150 minutes/week of moderate exercise, cut simple carbohydrates, and retest in 3-6 months.
❓ Frequently asked questions
What is the difference between FPG, 2hPG, RPG, and HbA1c?
FPG is measured after at least 8 hours of fasting and reflects basal glucose control. 2hPG is measured 2 hours after a glucose load and shows how the body handles carbohydrates. RPG can be taken at any time and is used for quick screening when symptoms are present. HbA1c reflects average blood glucose over the prior 2-3 months by measuring the percentage of hemoglobin bound to glucose. HbA1c is the most stable test and is not swayed by short-term factors like stress or recent meals.
What is prediabetes, and can it be reversed?
Prediabetes means blood glucose is higher than normal but not yet diabetic - FPG 100-125 mg/dL, 2hPG 140-199 mg/dL, or HbA1c 5.7-6.4%. Without intervention, 5-10% of people with prediabetes develop diabetes each year. The good news: it can often be reversed with 5-7% weight loss, a reduced-calorie diet, and 150 minutes/week of exercise. The Diabetes Prevention Program (DPP) showed this approach cut progression to diabetes by 58% over 3 years.
What is the HbA1c target for people with diabetes?
Per the ADA's Standards of Care, targets are individualized: under 7% for most adults with type 2 diabetes, under 6.5% for younger patients newly diagnosed and without comorbidities, and under 8% for older adults or those with a history of severe hypoglycemia, advanced vascular complications, or limited life expectancy. Each 1% drop in HbA1c reduces microvascular complications by 25-40% (UKPDS data).
How should I prepare for a fasting blood glucose test?
Fast for 8-12 hours before the test (water only), avoid vigorous exercise the night before, do not smoke the morning of the test, and keep taking your routine medications unless instructed otherwise. Schedule the test in the morning (7-9 AM) for standardized results. Avoid major stress and sleep deprivation, which can spuriously elevate glucose. Repeat the test on a separate day if the result is borderline.
Is normal blood glucose the same at every age?
The general thresholds are the same (FPG under 100 mg/dL, HbA1c under 5.7%), but clinical targets differ. Children and young adults aim for tighter control. Older adults (over 65) may have looser targets (HbA1c 7.5-8%) to avoid the risks of hypoglycemia. Pregnant women have stricter targets: FPG under 95, 2hPG under 120 mg/dL, to prevent complications of gestational diabetes. Infants and children should be managed by a pediatric endocrinologist.
📚 Sources & references
Last updated: May 11, 2026