Blood Sugar Checker

The same glucose number means different things at different times of day

If your meter shows 135, that is a high reading when you wake up before eating, but it is a number a person without diabetes can reach about an hour after lunch. That is why there is no single normal blood sugar, only a normal for each time you measure. After at least 8 hours without food, a fasting reading below 100 mg/dL is normal under American Diabetes Association (ADA) criteria. The ADA's 2001 consensus statement says glucose in people without diabetes rarely exceeds 140 mg/dL even after a meal. For adults managing diabetes, the ADA's general targets are 80 to 130 mg/dL before meals and a peak below 180 mg/dL after meals.

Enter readings from your meter into the seven time slots above (fasting, 2 hours after breakfast, before and 2 hours after lunch, before and 2 hours after dinner, and bedtime). Each reading is judged against the target for its own slot and drawn on a day curve over the normal or target band. Even a single reading gets a verdict and the distance to the limit. It is built for readings you take at home; to compare a lab report (fasting glucose, 75 g glucose tolerance test, A1C) with the diagnostic ranges, use the diabetes risk calculator.

Why measure at several times of day

A1C shows your average over about the past 2 to 3 months, but not when in the day glucose rises and falls. A fasting reading reflects what the liver released overnight, while an after-meal reading reflects the food you ate and the insulin response to it. The ADA statement describes glucose in people without diabetes as peaking about 60 minutes after a meal starts, rarely exceeding 140 mg/dL, and returning to pre-meal levels within 2 to 3 hours. Normal fasting glucose with a high, long-lasting after-meal peak will not show up in a single fasting test.

• When a checkup fasting value is close to 100: a few days of readings 2 hours after meals show whether glucose returns to normal after eating. This is a hint about whether to ask for lab testing, not a diagnosis.
• When you take diabetes medicine or insulin: pairing a before-meal and an after-meal reading shows which meal raises glucose the most. A few days of notes to bring to your visit help your care team adjust medicine and meals.
• When you feel shaky or sweaty: checking on the spot tells you whether you are below 70 mg/dL and whether to start treating low blood sugar.

How to use the checker

1. Pick whose targets to use: choose No diabetes diagnosis if you have never been diagnosed, or Managing diabetes if you have. The same number is judged against the normal range for the first and against treatment targets for the second, and the band on the chart changes with it.
2. Check the unit: choose mg/dL (United States, most of Asia and Latin America) or mmol/L (United Kingdom, Canada, Australia and several other countries), whichever your meter displays. Values already entered are converted when you switch the unit (mg/dL to whole numbers, mmol/L to one decimal place) and judged as shown; switching back restores what you typed.
3. Enter values: type each reading into the box for the time you took it. Each box sits directly under its column of the chart, so a dot appears as soon as you enter a value. Blank boxes are skipped, and a dashed line crosses the gap.
4. Read the result: the upper left shows the verdict and the distance to the limit for the reading you just entered or selected, and the upper right shows a summary of the day (how many readings are in range, the average, the highest and the lowest). Select another box or a chart column to switch to that reading. On first load, the most urgent reading is shown (low first, then very high, then high).
5. Read the chart: the gray band is the normal or target range for that slot, and the hatched area at the bottom is the hypoglycemia zone below 70. The dot shape carries the verdict: a circle is in range, an upward triangle is high and a downward triangle is low. The number beside each meal name is the rise from before the meal to 2 hours after.
6. Save it: Copy result copies the readings and verdicts as text, and Copy link copies an address that reopens this screen. Glucose values are placed only after the # in the address, so they are not sent to a server, and they are not saved in this browser.

Blood sugar ranges by time of day

These are the ranges the checker uses, in mg/dL. In mmol/L the same limits use the standard rounded values (70 = 3.9, 100 = 5.6, 126 = 7.0, 140 = 7.8, 180 = 10.0, 200 = 11.1).

The fasting limits match the ADA diagnostic criteria: 100 to 125 is the prediabetes range and 126 or higher is in the diabetes range. A diagnosis, however, is made from a laboratory plasma glucose that is confirmed on another day, so a home reading in these ranges is a signal to get tested, not a verdict. The 140 limit for non-fasting times follows the ADA statement that people without diabetes rarely go above 140 after eating, and 200 is the cutoff for diagnosing diabetes from a random glucose when classic symptoms such as thirst, frequent urination and weight loss are present.

The ADA Standards of Care 2026 list, for most nonpregnant adults, a pre-meal capillary plasma glucose of 80 to 130 mg/dL and a peak after-meal glucose below 180 mg/dL, along with an A1C below 7%. They also say after-meal readings should be taken 1 to 2 hours after the meal begins. These are general targets, so if your care team has set different numbers for you, theirs come first. A pre-meal reading of 70 to 79 is not hypoglycemia but sits below the target range, so it is shown as Below target. ADA's general adult targets (Section 6) give no separate bedtime goal, so the checker uses the 70 to 180 daily target range from the 2019 international consensus on reading continuous glucose monitor data, and splits out the above-250 zone that the same consensus counts separately as Very high.

This is the ADA classification. The checker marks anything below 70 as Low (Low (hypo) when you are managing diabetes) and anything below 54 as Very low (Level 2 low when you are managing diabetes).

When and how to measure so the ranges apply

• Count 2 hours from the first bite: counting from the end of the meal means measuring later and getting a lower number. The ADA asks for after-meal readings 1 to 2 hours after the start of the meal, so a 1-hour reading can also go in an after-meal box and be read against the same limit.
• Fasting means before anything to eat: the fasting range assumes at least 8 hours without food, so a reading after a late-night snack does not fit it.
• Repeat the same time for several days: a day's values shift with meals, activity and sleep. Comparing the same time over several days separates a one-off spike from a consistently high value.
• Meters are not exact: the international standard ISO 15197:2013 passes a meter if 95% of readings are within ±15 mg/dL below 100 mg/dL and within ±15% at 100 or above. For a true 140, that means readings from about 119 to 161, so do not draw conclusions from one or two values near a limit.
• Converting units: multiply mmol/L by 18 to get mg/dL (more exactly 18.016, since 1 mmol of glucose weighs 180.16 mg). The checker accepts whole numbers in mg/dL and one decimal place in mmol/L.

Example day curves

These are the values shown when the page loads (Example 1) and the values the Fill example button enters (Example 2), judged by the same rules as the checker.

Example 1 has 6 of 7 readings in the normal range and an average of 115. Only the reading 2 hours after lunch, 146, is above 140, by 6, and the rises from before the meal to after are +36 at breakfast, +51 at lunch and +35 at dinner. One reading over the line by this much can be within meter error, so the first step is to measure again over a few days with the same meal and timing.

Example 2 has 3 of 7 readings in target and an average of 149. The fasting and after-breakfast values are above target, glucose drops to 68 before dinner and then climbs to 210 after dinner, so the biggest swing of the day (+142) is in the evening, compared with +58 at breakfast and +62 at lunch. The checker puts the most urgent value, the low before dinner, at the top of the result and shows what to do about it. A record like this is useful to copy and show at a visit.

What to do with a low or high reading

• Below 70 mg/dL: the ADA advises that for most people 15 g of carbohydrate should be taken, glucose being the preferred treatment for a conscious person, and that glucose should be rechecked 15 minutes later. If it is still low after 15 minutes, repeat the treatment. People who use an automated insulin delivery system are advised a smaller amount, 5 to 10 g.
• Below 54, or confused or unable to treat yourself: this is Level 2, or Level 3 (severe) if you cannot recover without help. Ask someone nearby for help and contact emergency services or your care team.
• Above 250 while managing diabetes: the checker marks this as very high. If it keeps happening, or you have vomiting, fever or cannot keep fluids down, follow the sick-day plan your care team gave you, check ketones as they advised and contact them. The ADA notes that people prone to ketosis need urine or blood ketone monitoring during illness.
• High reading without a diabetes diagnosis: a home meter alone does not diagnose diabetes. If the same time keeps reading high over several days, ask a clinic for a fasting glucose and A1C test, and use the diabetes risk calculator to read the diagnostic ranges on the report. A random reading of 200 or more with symptoms should not wait for a routine visit.

Blood sugar targets differ by country

The glucose numbers are nearly the same everywhere, and the difference is in the A1C target: Korea sets 6.5% for type 2 diabetes, while the United States and Japan use 7.0% as the basic goal. Even normal fasting glucose varies: the United States and Korea use below 100, while Japan uses below 110 (100 to 109 is flagged as high-normal). This checker's English version uses US (ADA) criteria and the Japanese version uses Japan Diabetes Society criteria.

Common mistakes

• Counting 2 hours from the end of the meal: count from the first bite. Measuring later gives lower numbers and makes after-meal glucose look better than it was.
• Applying glucose tolerance test limits to an ordinary meal: the 2-hour limits of 140 and 200 apply after drinking 75 g of glucose, which is not the same amount or mix as a regular meal. That is why the checker calls an after-meal value of 140 or more only High, and does not label it impaired glucose tolerance.
• Deciding from one high reading: with the meter tolerance and the day's meal in mind, compare the same time over several days first.
• Reading mmol/L as mg/dL: 5.4 mmol/L is 97 mg/dL. The checker reports an error if a decimal is typed into the mg/dL box, and re-reads the text exactly as typed when you switch to mmol/L.
• Using the non-diabetic fasting range as a goal while managing diabetes: pushing glucose too low raises the risk of hypoglycemia. Follow the targets you set with your care team.

Limits and cautions

• These are adult ranges. In pregnancy, including gestational diabetes, targets are lower, and for children, teenagers and older adults a care team sets them individually, so do not use these limits as they are.
• A verdict is not a diagnosis. Diabetes is diagnosed by a clinician using a laboratory fasting glucose, a glucose tolerance test or A1C, with repeat testing.
• The 14-day time in range from a continuous glucose monitor is a different measure from a few fingerstick readings. The checker's "in range" count is only the number of values you entered.
• Glucose values go only after the # in a copied link, are not sent to a server and are not stored in this browser.

As of The glucose ranges and sources were checked on 2026-10-19.

Sources

• 01ADA: Standards of Care in Diabetes—2026, 6. Glycemic Goals, Hypoglycemia, and Hyperglycemic CrisesBefore-meal 80–130, peak after-meal below 180, A1C below 7%, hypoglycemia levels 70 and 54, after-meal readings 1–2 h from the start of the meal
• 02ADA: Standards of Care in Diabetes—2024, 6. Glycemic Goals and Hypoglycemia"For most individuals, 15 g carbohydrates should be ingested"; recheck glucose 15 min after; repeat if hypoglycemia persists; 5–10 g with automated insulin delivery
• 03ADA: Standards of Care in Diabetes—2026, 2. Diagnosis and Classification of DiabetesFasting glucose 126 or higher, 2-h OGTT 200 or higher, random 200 or higher with classic symptoms; fasting means at least 8 h without calories
• 04American Diabetes Association: Postprandial Blood Glucose (Diabetes Care 2001;24:775)In people without diabetes, glucose peaks about 60 minutes after a meal starts, rarely exceeds 140 mg/dl, and returns to pre-meal levels within 2–3 hours
• 05Battelino T et al.: Clinical Targets for Continuous Glucose Monitoring Data Interpretation (Diabetes Care 2019;42:1593)Target range 70–180 mg/dL, levels below 70 and below 54, above 180 and above 250
• 06Freckmann G et al.: Analytical Performance Requirements for Systems for Self-Monitoring of Blood Glucose (J Diabetes Sci Technol 2015)ISO 15197:2013: 95% of values within ±15 mg/dL below 100 mg/dL and ±15% at 100 or above
• 07Korean Diabetes Association: blood glucose control targetsGenerally 80–130 mg/dL before meals, below 180 two hours after meals, A1C below 6.5%
• 08Japan Diabetes Society: Diabetes Treatment Guide 2024, Chapter 2Figure 3: A1C below 6.0, 7.0 and 8.0%; fasting below 130 and 2-hour after-meal below 180 mg/dL as approximate guides
• 09PERKENI: Pedoman Pemantauan Glukosa Darah Mandiri 2021Table 1: pre-meal capillary glucose 80–130, 1–2 h after meal below 180
• 10redGDPS: Guía de diabetes tipo 2, Table 1 Objetivos de controlFasting 80–130, after meal below 180, A1C below 6.5% or 7–8%
• 11PERKENI: Pedoman Pengelolaan dan Pencegahan Diabetes Melitus Tipe 2 Dewasa di Indonesia 2021Table 11 control targets: A1C below 7% or individualized, pre-meal 80–130, 2 h after meals below 180

Frequently asked questions

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