A simple blood sugar log with targets, time in range and an estimated A1c
This blood sugar log lets you record finger-prick or meter glucose readings in mg/dL or mmol/L, say when each was taken — fasting, before a meal, one to two hours after, at bedtime or at another time — and see at once whether it sits inside your target range. Switch units at any time; every reading, target and chart follows.
Over a period you choose, the log shows your average glucose, the share of readings in range, how many were low or high, the average for each time of day and an estimated A1c worked out with the ADAG formula. A colour-coded chart and a printable report (paper, PDF or PNG) make it easy to discuss patterns with your doctor, nurse or diabetes educator. Readings are stored in this browser only, and you can export or import them as CSV.
The log is informational and not medical advice. Targets should be agreed with your care team, and an estimate from spot readings is not a laboratory HbA1c.
How to use the Blood Sugar Log
- Pick mg/dL (US, India) or mmol/L (UK, Europe, Australia). The quick converter turns one into the other.
- Enter the reading, choose When it was taken, adjust the date and time if needed and press Add reading.
- Open Target ranges and enter the ranges your doctor gave you, or keep the labelled defaults.
- Choose a Period to see averages, time in range and the estimated A1c, and look at the chart for patterns after meals or overnight.
- Before an appointment, press Print report or Download PDF. Use Export CSV as a backup.
Blood Sugar Log features
mg/dL ↔ mmol/L
Uses 18.016 mg/dL per mmol/L (from glucose’s molar mass of 180.16 g/mol), so 100 mg/dL = 5.55 mmol/L.
Meal context
Fasting, before meal, after meal, bedtime or other — each with its own editable target.
Time in range
The percentage of readings inside their target, plus the share below 70 and above 180 mg/dL.
Estimated A1c
From your average glucose with the ADAG equation, shown as a percentage and in mmol/mol, clearly labelled as an estimate.
Chart and report
Readings coloured by target over a shaded 70–180 band, and a printable report.
CSV in and out
Exports both units and the target status; imports files with mg/dL or mmol/L columns and skips duplicates.
Converting between mg/dL and mmol/L
To convert mg/dL to mmol/L divide by 18.016; to convert mmol/L to mg/dL multiply by 18.016. Many charts round the factor to 18, which barely changes results.
| mg/dL | mmol/L | Common meaning (adults with diabetes) |
|---|---|---|
| 54 | 3.0 | Clinically significant low (level 2) |
| 70 | 3.9 | Low threshold (level 1) |
| 80–130 | 4.4–7.2 | Typical before-meal target |
| 180 | 10.0 | Upper end of after-meal target and of time in range |
| 250 | 13.9 | Very high |
Blood sugar chart: normal, prediabetes and diabetes ranges
The chart and checker use the ADA Standards of Care in Diabetes—2026. For diagnosis (Section 2, Tables 2.1–2.2), a lab fasting plasma glucose below 100 mg/dL (5.6 mmol/L) is normal, 100–125 (5.6–6.9) is prediabetes and 126 (7.0) or more is in the diabetes range; two hours after a 75 g glucose drink the lines are 140 (7.8) and 200 (11.1); for A1C they are 5.7% and 6.5%. A random glucose of 200 (11.1) or more counts only with classic symptoms, and without unequivocal high glucose a diagnosis needs two abnormal results.
For people with diabetes (Section 6, Table 6.3) common targets are A1C below 7%, 80–130 mg/dL before meals and below 180 mg/dL one to two hours after the start of a meal. The chart by age adds older-adult goals (Section 13), children and teens (Section 14) and pregnancy (Section 15).
How the estimated A1c is calculated
The A1c-Derived Average Glucose (ADAG) study (Nathan and colleagues, Diabetes Care, 2008) found the relationship average glucose (mg/dL) = 28.7 × A1c − 46.7. Turned around, A1c ≈ (average glucose + 46.7) ÷ 28.7. An average of 154 mg/dL (8.5 mmol/L) therefore corresponds to an A1c of about 7.0%, or 53 mmol/mol on the IFCC scale.
The estimate is only as good as the readings behind it. Spot checks cluster around mealtimes and mornings, so they can over- or under-represent the hours between. Continuous glucose monitors use a related measure, the glucose management indicator (GMI). Always rely on your laboratory HbA1c for decisions.
Making your log more useful
- Test at consistent times, such as fasting and two hours after your largest meal.
- Note food, activity, illness or a missed dose; patterns often show in the notes first.
- Pair readings with medicine times from the medication schedule maker, and if you also monitor blood pressure, keep it in the blood pressure log.
- For meal planning, the macro calculator estimates carbohydrate, protein and fat targets.
Blood Sugar Log FAQ
What is a normal blood sugar level?
For adults without diabetes, fasting glucose is usually 70–99 mg/dL (3.9–5.5 mmol/L). For people with diabetes, a common before-meal target is 80–130 mg/dL and under 180 mg/dL one to two hours after eating, but your own targets may differ.
Does normal blood sugar change with age?
The diagnostic ranges are the same for every adult. What changes with age is the target once someone has diabetes: the ADA allows a higher A1C goal — below 8.0% — and a fasting range of 90–150 mg/dL for older adults with several health problems.
How do I convert mg/dL to mmol/L?
Divide by 18.016 (or about 18). For example, 100 mg/dL ÷ 18.016 = 5.55 mmol/L, and 7 mmol/L × 18.016 = 126 mg/dL. The blood sugar log has a quick converter at the top.
How accurate is the estimated A1c?
It is a rough guide. It assumes your logged readings represent your whole day, which spot checks rarely do, and conditions such as anaemia also affect real A1c. Use it to watch trends, and compare it with your lab result.
What does time in range mean here?
The percentage of your logged readings that fall inside the target for their context. International consensus for continuous monitors uses 70–180 mg/dL and aims for more than 70% of the day; with finger-prick readings the figure is an approximation.
Is my data private?
Yes. Readings stay in your browser’s storage on this device and are never uploaded. Clearing site data removes them, so export a CSV from time to time.
What should I do with a very low or very high reading?
Follow the plan your care team gave you. Below 70 mg/dL usually means taking fast-acting sugar and re-checking; very high readings with vomiting, drowsiness or ketones need urgent medical advice.