Blood Sugar Calculator

It depends on when you tested. For a fasting reading (at least 8 hours without food), normal is under 100 mg/dL (5.6 mmol/L). For a reading taken 2 hours after a meal, normal is under 140 mg/dL (7.8 mmol/L). Anything below 70 mg/dL (3.9 mmol/L) is treated as low blood sugar regardless of when you tested, since a low reading needs attention right away.

Prediabetes means your blood sugar is higher than normal but not yet in the diabetes range — fasting 100 to 125 mg/dL, or 140 to 199 mg/dL two hours after eating. It's a warning sign, not a life sentence: research from the Diabetes Prevention Program found that losing around 5 to 7 percent of body weight, alongside regular activity, roughly halved the chance of progressing to type 2 diabetes.

No, and this calculator won't tell you that it can. A single reading in the diabetes range (126 mg/dL or higher fasting, or 200 mg/dL or higher after a meal) is a prompt to get properly tested, not a diagnosis by itself. Medical guidelines require the result to be confirmed with a repeat test or a second type of test, unless you also have clear symptoms like unusual thirst, frequent urination, and unexplained weight loss.

They're just two different units for the same measurement, similar to measuring your height in inches versus centimeters. mg/dL is used in the US and much of Asia; mmol/L is used in the UK, Canada, Europe, and Australia. To convert, divide mg/dL by 18.0156 to get mmol/L, or multiply mmol/L by 18.0156 to get mg/dL — that number comes from the molar mass of glucose, which is why it isn't a round figure.

Some difference is expected and normal. Home meters are generally allowed a margin of about 15 percent compared with a laboratory reference, which is usually fine for everyday tracking but can occasionally shift a reading across a threshold like the prediabetes cutoff. Stress, illness, certain medications, and recent food intake can also move your number. If a reading surprises you, retest and talk to a healthcare provider rather than relying on one result.

Not exactly. The 140/200 mg/dL thresholds are the ADA's formal oral glucose tolerance test (OGTT) categories, measured 2 hours after drinking a standardized 75 g glucose solution at a clinic. A home glucometer reading taken 2 hours after an ordinary meal is a related but less standardized measurement — meal size and carbohydrate content vary far more than a fixed glucose drink, so the same number carries more uncertainty in that context. Use it as a rough guide against these bands, not as a diagnostic OGTT result. If you actually had a clinic OGTT with the standard glucose drink, these thresholds apply directly.