Blood sugar levels chart and range checker

How the checker works

The checker takes one glucose value and converts it to mg/dL using 18.016, the factor that relates glucose in mmol/L to mg/dL. It then compares the value with ADA cutoffs and a standard reference chapter on classification and diagnosis. For fasting, the cutoffs are under 70 mg/dL for low, 70 to 99 for the usual range, 100 to 125 for the prediabetes range, and 126 or higher for the diabetes range. For a 2-hour glucose tolerance test, the usual range ends at 139, the prediabetes range is 140 to 199, and the diabetes range starts at 200 (Genuth et al.; ADA Standards of Care 2025, section 2).

A random reading does not have the same clean bands. A random plasma glucose of 200 mg/dL or higher is diagnostic only when it comes with classic symptoms such as unusual thirst, frequent urination, or weight loss (Genuth et al.). Without symptoms, a high random reading needs confirmation. A random value between 140 and 199 cannot be assigned to a category because food and timing are unknown.

How to read your result

Read the band label first, then the sentence under it. The label names the range, and the sentence explains what it generally means and when to talk with a doctor. The same number appears in mg/dL and mmol/L so you can compare it with your meter or report.

A result in the usual range does not rule out diabetes. A result in the prediabetes range is a reason to arrange a lab test, not a diagnosis. A result in the diabetes range is not a diagnosis from one home reading. The ADA recommends confirming an abnormal test with a repeat test (ADA Standards of Care 2025, section 2). Your doctor may choose fasting plasma glucose, a 2-hour glucose tolerance test, or an A1c test. Each test measures something different, and they do not always agree (Genuth et al.).

A low reading is treated as its own category. The ADA defines level 1 hypoglycemia as a glucose below 70 mg/dL (ADA Standards of Care 2025, section 6). If you take a medicine that can lower blood sugar, follow the low blood sugar plan your care team gave you. If you have confusion, fainting, or a seizure, seek emergency care now. If you do not take such a medicine, a reading under 70 is still worth mentioning to a doctor, especially if it happens more than once.

Why a meter and a lab can differ

Home meters usually measure capillary blood from a fingertip, while a lab measures glucose in venous plasma. In a study of 407 people having glucose tolerance tests, capillary meter readings averaged higher than venous plasma readings, especially 2 hours after the glucose load (Priya et al.). Meter models also vary. A review of 143 meter systems found that not every meter met the accuracy standards it was checked against, and manufacturer-supported studies were more likely to report a pass than independent studies (King et al.).

That is why this checker uses the standard lab cutoffs but tells you they are not a diagnosis. A home reading of 126 mg/dL is not the same event as a lab fasting plasma glucose of 126 mg/dL. The number can start a conversation; it cannot replace the lab test your doctor would use. Timing, food, hydration, illness, and the meter itself can all move a single reading.

What to bring to a doctor

Bring the meter or the report, the reading, the unit, the date and time, and when you last ate. Write down any symptoms, especially unusual thirst, frequent urination, blurred vision, weight loss, shakiness, sweating, confusion, or fainting. Bring a current medicine list and any earlier glucose or A1c results. For repeated readings, a log with the time and context is more useful than one number.

Ask what test would be appropriate for you and whether the reading should be repeated. Do not stop or change any medicine on your own. If you have symptoms of very high or very low blood sugar, use the urgent care guidance above rather than waiting for an appointment.

Frequently asked questions

Is 100 to 125 mg/dL fasting prediabetes?

That is the ADA prediabetes range for a lab fasting plasma glucose test (Genuth et al.). It is not a diagnosis from one meter reading, and a confirmatory test is usually needed.

Can I use this checker 2 hours after eating?

Yes, choose the after-meal context. The 140 and 200 mg/dL cutoffs come from a standardized 75 g glucose tolerance test, not an ordinary meal. A home reading after your own meal is useful context, but not a glucose tolerance test result.

Does one high reading mean I have diabetes?

No. One reading does not diagnose diabetes. The ADA recommends confirmation of an abnormal test, and a home meter is not a lab plasma test (ADA Standards of Care 2025, section 2). Contact a doctor to plan follow-up testing.

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

Divide mg/dL by 18.016 to get mmol/L. For example, 126 divided by 18.016 is about 7.0 mmol/L. To go the other way, multiply mmol/L by 18.016.

Why is my meter reading different from my lab result?

Meters measure capillary blood and labs usually measure venous plasma. Capillary readings can run higher, especially after a glucose load (Priya et al.). Meter accuracy also varies between models and studies (King et al.). Use the lab result when your doctor classifies a test.

When should I seek urgent care?

Seek urgent care for a very high reading with vomiting, confusion, or trouble breathing, or a low reading with confusion, fainting, or a seizure. These are signs of a hyperglycemic or hypoglycemic emergency and should not wait for an appointment (Fayfman et al.; ADA Standards of Care 2025, section 6).

For a neutral comparison of blood sugar supplement labels and their evidence, see our blood sugar supplement comparison.

Read more about normal blood sugar levels by age, fasting blood sugar levels, blood sugar after eating, and the prediabetes range. If you are working from A1c, see what A1c is, the A1c chart, and A1c versus glucose. For low readings, see low blood sugar symptoms. For very high readings, see blood sugar over 400. For general ways to improve glucose, see how to lower A1c.