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Blood Sugar Calculator

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Enter your blood glucose reading and test type to check which category it falls into, based on American Diabetes Association guidelines.

Blood Sugar Calculator

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Category
Normal
Range used
70-99 mg/dL
Informational only, not a diagnosis. A formal diagnosis typically requires a lab test, sometimes an A1C test or a repeat reading.

The classification

Fasting (at least 8 hours without food): Low: under 70 mg/dL Normal: 70-99 mg/dL Prediabetes range: 100-125 mg/dL Diabetes range: 126+ mg/dL Non-fasting / Random (any time of day): Low: under 70 mg/dL Normal: under 140 mg/dL Elevated: 140-199 mg/dL Diabetes range: 200+ mg/dL
Example

A fasting reading of 92 mg/dL falls in the Normal range (70-99) - but that same 92 mg/dL reading taken 2 hours after a meal would also read Normal, since the non-fasting threshold for normal is under 140.

Step-by-step guide

  1. Note when you last ate. If it's been 8 or more hours, use "Fasting" - otherwise use "Non-fasting / Random."
  2. Enter your glucose reading in mg/dL from your meter or lab result. If your result is in mmol/L, multiply by 18 to convert to mg/dL first.
  3. Read your category and the specific range it falls into.

How this relates to A1C

A1C is a separate but related test that measures your average blood sugar over the past 2-3 months, rather than a single point-in-time reading like this calculator uses. An A1C of 5.7-6.4% corresponds to the prediabetes range, and 6.5% or higher corresponds to the diabetes range - broadly similar categories to the fasting glucose ranges above, but measuring a longer-term average rather than today's reading.

Common mistakes

Using fasting thresholds for a reading taken after eating - a normal post-meal reading is expected to be higher than a normal fasting reading, so comparing them with the same cutoff overstates the concern.
Treating a single elevated reading as a diagnosis - blood sugar naturally fluctuates, and a proper diagnosis typically involves a lab-based test, sometimes repeated or paired with an A1C test.

Frequently asked questions

What's the difference between fasting and non-fasting thresholds?

Blood sugar naturally rises after eating, so the "normal" ceiling is higher for non-fasting readings (under 140 mg/dL) than for fasting readings (under 100 mg/dL). Using the wrong threshold for your situation will misclassify a genuinely normal result.

Is one prediabetes-range reading a diagnosis?

Not on its own - a formal diagnosis typically involves a lab-based test (not a home meter), sometimes confirmed with a repeat test or an A1C test measuring your average blood sugar over 2-3 months.

How do I convert mmol/L to mg/dL?

Multiply your mmol/L reading by 18 to get mg/dL (for example, 5.5 mmol/L x 18 = 99 mg/dL). Most of the US uses mg/dL, while most other countries use mmol/L.

Is a "Normal" reading here always healthy?

The standard clinical ranges above are a useful general guide, though some research suggests fasting glucose in the lower half of the normal range is associated with somewhat lower long-term risk than the upper half. Discuss your specific numbers and trends with a doctor.

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