How to Convert Magnesium Units
Serum magnesium is reported three ways: mg/dL (US), mmol/L (SI) and mEq/L (equivalents). The mass-to-molar factor comes from magnesium's atomic weight of 24.305, and the mEq step uses its valence of 2.
Magnesium mmol/L = magnesium mg/dL × 0.4114 Magnesium mEq/L = magnesium mmol/L × 2 Magnesium mEq/L = magnesium mg/dL × 0.8228 Magnesium Conversion Chart
| mg/dL | mmol/L | mEq/L | Context |
|---|---|---|---|
| 1.5 mg/dL | 0.62 mmol/L | 1.23 mEq/L | Low (hypomagnesemia) |
| 1.7 mg/dL | 0.70 mmol/L | 1.40 mEq/L | Lower normal |
| 2.0 mg/dL | 0.82 mmol/L | 1.65 mEq/L | Normal |
| 2.2 mg/dL | 0.91 mmol/L | 1.81 mEq/L | Upper normal |
| 3.0 mg/dL | 1.23 mmol/L | 2.47 mEq/L | High (hypermagnesemia) |
| 4.0 mg/dL | 1.65 mmol/L | 3.29 mEq/L | High |
Magnesium Reference Ranges
| Category | mg/dL | mmol/L | mEq/L |
|---|---|---|---|
| Low (hypomagnesemia) | Below 1.7 mg/dL | Below 0.7 mmol/L | Below 1.4 mEq/L |
| Normal | 1.7 – 2.2 mg/dL | 0.7 – 0.9 mmol/L | 1.4 – 1.8 mEq/L |
| High (hypermagnesemia) | Above 2.2 mg/dL | Above 0.9 mmol/L | Above 1.8 mEq/L |
There is no single international consensus range, so always compare against your own laboratory's interval.
Low Magnesium (Hypomagnesemia)
A magnesium below about 1.7 mg/dL (0.7 mmol/L) is low. It commonly travels with low potassium and low calcium, and low magnesium can make those hard to correct until the magnesium itself is replaced. Symptoms include cramps, weakness, tremor and heart-rhythm disturbances.
High Magnesium (Hypermagnesemia)
High magnesium is much less common and is usually related to reduced kidney function or magnesium-containing antacids and laxatives. Marked elevations can lower blood pressure and reflexes and, when severe, affect the heart.
Worked Example
Suppose a report shows 0.6 mmol/L and you want mg/dL:
0.6 × 2.43 = 1.46 mg/dL (and 0.6 × 2 = 1.2 mEq/L) 1.46 mg/dL is below the normal range — consistent with hypomagnesemia.
Frequently Asked Questions
How do you convert magnesium mg/dL to mmol/L?
Multiply mg/dL by 0.4114. For example, 2.0 mg/dL is about 0.82 mmol/L.
How do you get mEq/L?
Multiply mmol/L by 2 (magnesium is divalent), or mg/dL by 0.8228.
What is a normal magnesium level?
About 1.7–2.2 mg/dL (0.7–0.9 mmol/L, 1.4–1.8 mEq/L).
What is low magnesium?
Below about 1.7 mg/dL (0.7 mmol/L) is hypomagnesemia.
References
- European Journal of Nutrition — Standardization of serum magnesium reference ranges.
- Magnesium factor 0.4114 (atomic weight 24.305); valence 2 for mEq/L (mmol/L × 2).
Conclusion
Converting magnesium is a ×0.4114 for mmol/L and a ×2 (valence) for mEq/L. The value matters most at the low end — hypomagnesemia is common and often hides behind stubborn low potassium and calcium. Interpret results with your healthcare provider.