blood glucose calculator

Use this blood glucose calculator to convert between mg/dL and mmol/L, interpret a reading based on timing, and optionally estimate A1C from average glucose. It is built for quick educational use and does not replace professional medical advice.

How this blood glucose calculator helps

Most people see glucose values in one of two units: mg/dL (common in the U.S.) or mmol/L (common in many other countries). This tool instantly converts both ways, then compares your number against common reference ranges for fasting, post-meal, or random tests.

That matters because the same number can mean different things depending on when it was taken. A value that looks okay after eating may be high if it was measured during fasting. Context is everything.

Reference ranges used by the calculator

Fasting glucose

• Below 70 mg/dL (3.9 mmol/L): low blood sugar (hypoglycemia range)
• 70–99 mg/dL (3.9–5.5 mmol/L): typical fasting range
• 100–125 mg/dL (5.6–6.9 mmol/L): prediabetes range
• 126 mg/dL or higher (7.0 mmol/L or higher): diabetes-range result (requires medical confirmation)

2-hour post-meal / oral glucose test style interpretation

• Below 140 mg/dL (7.8 mmol/L): typical response
• 140–199 mg/dL (7.8–11.0 mmol/L): elevated / prediabetes range
• 200 mg/dL or higher (11.1 mmol/L or higher): diabetes-range result (needs formal confirmation)

Random glucose

• Below 70 mg/dL: low
• 70–139 mg/dL: often acceptable in many situations
• 140–199 mg/dL: elevated; follow-up may be useful
• 200 mg/dL or higher: can indicate diabetes, especially with symptoms like frequent urination, thirst, and unexplained weight loss

Unit conversion formula

If you ever need manual conversion:

• mmol/L = mg/dL ÷ 18
• mg/dL = mmol/L × 18

The calculator performs this conversion automatically and displays both units together for easy comparison.

Estimated A1C from average glucose

If you enter a true average glucose value (not a single reading), the tool also estimates A1C using the standard equation:

A1C = (Average Glucose + 46.7) ÷ 28.7 (with average glucose in mg/dL)

Remember: this estimate is useful for trend tracking, but a lab A1C test remains the clinical standard.

What can affect your blood sugar reading?

• Meal timing and carbohydrate amount
• Stress, illness, and poor sleep
• Physical activity level
• Medication timing and dose
• Hydration and alcohol intake
• Meter technique (strip quality, hand washing, calibration)

When to seek medical help

Talk with a clinician if your readings are repeatedly outside target ranges. Seek urgent care for severe symptoms (confusion, vomiting, trouble breathing, fainting), very high sustained glucose, or severe low blood sugar that does not improve promptly.

This page is educational and cannot diagnose disease. Use it as a companion tool alongside your healthcare provider’s recommendations.