How to Convert Phosphate mg/dL to mmol/L
Serum phosphate is reported in mg/dL in the US and mmol/L in most other countries, and is measured as elemental phosphorus. The conversion factor is 0.3229, from phosphorus's atomic weight of 30.97.
Phosphate mmol/L = phosphate mg/dL × 0.3229 Phosphate mg/dL = phosphate mmol/L × 3.1 Phosphate mg/dL to mmol/L Chart
| mg/dL | mmol/L | Context |
|---|---|---|
| 1.0 mg/dL | 0.32 mmol/L | Severe low (symptomatic) |
| 2.5 mg/dL | 0.81 mmol/L | Lower normal |
| 3.5 mg/dL | 1.13 mmol/L | Normal (mid) |
| 4.5 mg/dL | 1.45 mmol/L | Upper normal |
| 5.0 mg/dL | 1.61 mmol/L | High (hyperphosphatemia) |
| 7.0 mg/dL | 2.26 mmol/L | Marked high |
mmol/L to mg/dL Reverse Chart
| mmol/L | mg/dL |
|---|---|
| 0.32 mmol/L | 1.0 mg/dL |
| 0.81 mmol/L | 2.5 mg/dL |
| 1.13 mmol/L | 3.5 mg/dL |
| 1.45 mmol/L | 4.5 mg/dL |
Phosphate Reference Ranges
| Category | mg/dL | mmol/L |
|---|---|---|
| Severe low | Below 1.0 mg/dL | Below 0.32 mmol/L |
| Low (hypophosphatemia) | Below 2.5 mg/dL | Below 0.81 mmol/L |
| Normal (adult) | 2.5 – 4.5 mg/dL | 0.81 – 1.45 mmol/L |
| High (hyperphosphatemia) | Above 4.5 mg/dL | Above 1.45 mmol/L |
Children and infants normally run 30–50% higher than adults because of growth.
Low Phosphate (Hypophosphatemia)
Low phosphate is common in hospital, and its classic trigger is refeeding syndrome — when nutrition is restarted after a period of starvation and cells rapidly take up phosphate. Other causes include alcohol use and the treatment of diabetic ketoacidosis. It becomes important below about 1.0 mg/dL (0.32 mmol/L), where muscle weakness — including of the breathing muscles — can develop.
High Phosphate (Hyperphosphatemia)
The most common cause of high phosphate is reduced kidney function, because the kidneys are what clear it. In chronic kidney disease, phosphate is watched and managed closely, since a high calcium–phosphate product contributes to bone disease and vascular calcification.
Worked Example
Suppose a report shows 0.6 mmol/L and you want mg/dL:
0.6 × 3.1 = 1.86 mg/dL 1.86 mg/dL is below the normal range — hypophosphatemia. Converting the other way, 4.5 mg/dL is about 1.45 mmol/L, the upper limit.
Frequently Asked Questions
How do you convert phosphate mg/dL to mmol/L?
Multiply mg/dL by 0.3229. For example, 3.5 mg/dL is about 1.13 mmol/L.
Is phosphate the same as phosphorus?
On a blood test, yes — it is reported as elemental phosphorus.
What is a normal phosphate level?
About 2.5–4.5 mg/dL (0.81–1.45 mmol/L) in adults.
What causes low phosphate?
Refeeding syndrome, alcohol use and DKA treatment are common causes.
References
- NCBI / StatPearls — Hypophosphatemia.
- Phosphate (phosphorus) factor 0.3229 (atomic weight 30.97); adult reference range 2.5–4.5 mg/dL.
Conclusion
Converting phosphate between mg/dL and mmol/L is a ×0.3229. The value matters most at the extremes — low phosphate in refeeding, high phosphate in kidney disease. Interpret results with calcium and your healthcare provider.