Blood Sugar Converter
Convert blood glucose between mg/dL and mmol/L with the clinical factor 18.
What it does
Meters and lab slips report glucose in two units: mg/dL across the US and mmol/L across most of the rest of the world. The bridge is division by 18 one way and multiplication the other, so 180 mg/dL reads 10 mmol/L everywhere.
The tool above converts either direction and prints the round trip beside it. The default 180 mg/dL gives 10 mmol/L with 180 mg/dL back, while 126 mg/dL gives 7 mmol/L, the fasting diabetes threshold.
Both factors rest on the same chemistry. Clinics use 18 for head math while the exact 18.01559 falls out of the NIST glucose molar mass of 180.1559, and at one decimal place both agree on every standard threshold.
This page changes units the way a temperature converter changes scales; it never averages or diagnoses. Averages live on the A1C page, and any reading that worries you belongs with a clinician, not a converter.
How to use
- Type the glucose number.
- Pick the unit it carries now.
- Pick the unit you want back.
- Read converted first, round trip beside it.
- Compare against thresholds only in matching units.
- Log which unit each entry uses to stop mixups.
Formula
- 18
- Clinical conversion factor used by ADA guidance.
- 18.01559
- Exact factor from the NIST glucose molar mass.
- round trip
- Converting back must return the starting number.
mmol/L prints to 1 decimal and mg/dL to whole numbers, matching meter and lab habits. The exact factor shifts results by about half a percent, inside display rounding.
Worked example
Example: 180 mg/dL
Defaults: value 180, from mg/dL, to mmol/L.
- Divide: 180 / 18.01559 = 9.9913.
- Display: 10 mmol/L at 1 decimal.
- Round trip: 10 x 18.01559 = 180.16, shown as 180 mg/dL.
- Clinical check: 180 / 18 = 10 exactly.
- Tool shows 10 mmol/L with 180 mg/dL back.
Reference table
| mg/dL | mmol/L | Meaning |
|---|---|---|
| 70 | 3.9 | Low end of normal fasting |
| 99 | 5.5 | High end of normal fasting |
| 100 to 125 | 5.6 to 6.9 | Impaired fasting band |
| 126 | 7.0 | Diabetes fasting threshold |
| 200 | 11.1 | Diabetes random threshold |
Limits
- Unit math only; no averages or diagnosis.
- Meter error of 10 to 15% dwarfs factor choice.
- Fasting and random thresholds differ; context rules.
- A1C averages need their own page and formula.
Common mistakes
- Multiplying mg/dL by 18 instead of dividing.
- Comparing a mmol/L reading against mg/dL charts.
- Quoting 4 decimals as if meters read them.
- Treating one high reading as a diagnosis.
- Mixing units inside one logbook column.
Try it yourself
Quick checks. Answers sit tucked under each question.
126 mg/dL in mmol/L?
7 mmol/L, the fasting diabetes threshold.
10 mmol/L in mg/dL?
180 mg/dL.
99 mg/dL in mmol/L?
5.5 mmol/L, top of normal fasting.
Questions
What is 180 mg/dL in mmol/L?
10 mmol/L.
Why 18?
Glucose molar mass 180.1559 makes 1 mmol/L equal about 18 mg/dL; clinics round to 18.
Exact or clinical factor?
Both: exact 18.01559 for math, 18 for head checks; displays agree.
Normal fasting range?
70 to 99 mg/dL, which is 3.9 to 5.5 mmol/L.
Diabetes thresholds?
126 mg/dL (7 mmol/L) fasting, 200 mg/dL (11.1 mmol/L) random, with clinical context.
Does this replace A1C?
No. A1C averages months; this converts single readings between units.