The factor depends on what was measured, not on the units
Both units describe the same concentration, but converting between them needs the molecular weight of the substance. Glucose, cholesterol and triglycerides each have their own factor, so a single "multiply by 18" only works for glucose.
The factor for each blood test
| Analyte | mmol/L → mg/dL | mg/dL → mmol/L |
|---|---|---|
| Glucose | × 18.0 | ÷ 18.0 |
| Total / LDL / HDL cholesterol | × 38.67 | ÷ 38.67 |
| Triglycerides | × 88.57 | ÷ 88.57 |
mmol/L is the standard in the UK, Canada, Australia and most of Europe; mg/dL is used in the US. A lipid panel from one country will use one unit throughout.
Common glucose and cholesterol values, both ways
| Reading | mmol/L | mg/dL | Meaning |
|---|---|---|---|
| Glucose, normal fasting | < 5.6 | < 100 | Healthy |
| Glucose, prediabetes | 5.6 – 6.9 | 100 – 125 | Raised |
| Glucose, diabetes (fasting) | ≥ 7.0 | ≥ 126 | Diagnostic |
| Total cholesterol, desirable | 5.2 | 200 | Target |
| Total cholesterol, high | 6.2 | 240 | Raised |
| Triglycerides, normal | 1.13 | 100 | Healthy |
Common questions
Why is the conversion factor different for glucose and cholesterol?
The factor comes from the substance molecular weight, and each substance weighs something different. Glucose uses 18, cholesterol uses 38.67, triglycerides use 88.57. Use the wrong factor and the number is meaningless, so always match the factor to what was measured.
How do I convert glucose from mmol/L to mg/dL in my head?
Multiply by 18. A reading of 5.5 mmol/L is about 99 mg/dL, and 7.0 mmol/L is 126 mg/dL, the fasting diabetes threshold. The exact factor is 18.0156, but 18 is close enough for everyday use.
My result is 7.5 mmol/L glucose. Is that high?
That equals 135 mg/dL. Normal fasting glucose is under 5.6 mmol/L (100 mg/dL), so 7.5 sits above the diabetes threshold of 7.0 mmol/L (126 mg/dL) for a fasting sample. Check with your doctor rather than reading this off a converter.
