Phosphate (phosphorus) conversion: to convert phosphate from mmol/L to mg/dL, multiply by 3.1 (exactly 3.097). To convert phosphorus from mg/dL to mmol/L, divide by 3.1 (or multiply by 0.323). Example: 1.4 mmol/L phosphate = 4.34 mg/dL.
Phosphate (PO₄³⁻, as P) Calculator
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Phosphate and Phosphorus: The Same Blood Test
Lab reports call this test serum phosphate, phosphorus, inorganic phosphate, PO4 or “phos”. In blood tests they all mean the same thing and use the same conversion factor, because laboratories measure phosphate but report it as phosphorus (molar mass 30.97 g/mol). That is why the phosphate factor is 3.1, not the much larger number you would get from the weight of a whole phosphate ion.
Phosphorus is also called fosforo on Italian and Spanish lab reports and phosphore on French ones; the conversion is identical.
Phosphate Conversion Factor
| Convert | Phosphate / phosphorus formula | Example |
|---|---|---|
| mmol/L to mg/dL | mg/dL = mmol/L × 3.097 | 1.0 mmol/L = 3.10 mg/dL |
| mg/dL to mmol/L | mmol/L = mg/dL ÷ 3.097 (or × 0.3229) | 4.5 mg/dL = 1.45 mmol/L |
| mmol to mg (amount) | mg = mmol × 30.97 | 1 mmol phosphorus = 30.97 mg |
| mg to mmol (amount) | mmol = mg ÷ 30.97 | 250 mg phosphorus = 8.07 mmol |
Many sources round the factor to 3.1 (mmol/L to mg/dL) and 0.32 (mg/dL to mmol/L). The difference is too small to matter clinically.
How to Convert Phosphate mmol/L to mg/dL
- Find the phosphate or phosphorus result on your report and check the unit.
- If it is in mmol/L, multiply by 3.097 (or 3.1).
- If it is in mg/dL and you need mmol/L, divide by 3.097.
Worked examples: 0.8 mmol/L × 3.097 = 2.48 mg/dL · 1.4 mmol/L × 3.097 = 4.34 mg/dL · 2.5 mmol/L × 3.097 = 7.74 mg/dL.
Phosphate Conversion Chart: mmol/L to mg/dL
| Phosphate (mmol/L) | Phosphorus (mg/dL) |
|---|---|
| 0.3 mmol/L | 0.93 mg/dL |
| 0.5 mmol/L | 1.55 mg/dL |
| 0.6 mmol/L | 1.86 mg/dL |
| 0.7 mmol/L | 2.17 mg/dL |
| 0.8 mmol/L | 2.48 mg/dL |
| 0.9 mmol/L | 2.79 mg/dL |
| 1 mmol/L | 3.10 mg/dL |
| 1.1 mmol/L | 3.41 mg/dL |
| 1.2 mmol/L | 3.72 mg/dL |
| 1.3 mmol/L | 4.03 mg/dL |
| 1.4 mmol/L | 4.34 mg/dL |
| 1.45 mmol/L | 4.49 mg/dL |
| 1.5 mmol/L | 4.65 mg/dL |
| 1.6 mmol/L | 4.96 mg/dL |
| 1.8 mmol/L | 5.58 mg/dL |
| 2 mmol/L | 6.19 mg/dL |
| 2.5 mmol/L | 7.74 mg/dL |
| 3 mmol/L | 9.29 mg/dL |
Phosphorus mg/dL to mmol/L Conversion
To convert phosphorus or phosphate from mg/dL to mmol/L, divide by 3.097. For example, 4.5 mg/dL ÷ 3.097 = 1.45 mmol/L, the usual upper limit of normal. You can also use the phosphate mg/dL to mmol/L converter.
| Phosphorus (mg/dL) | Phosphate (mmol/L) |
|---|---|
| 1.0 mg/dL | 0.32 mmol/L |
| 1.5 mg/dL | 0.48 mmol/L |
| 2.0 mg/dL | 0.65 mmol/L |
| 2.5 mg/dL | 0.81 mmol/L |
| 3.0 mg/dL | 0.97 mmol/L |
| 3.5 mg/dL | 1.13 mmol/L |
| 4.0 mg/dL | 1.29 mmol/L |
| 4.5 mg/dL | 1.45 mmol/L |
| 5.0 mg/dL | 1.61 mmol/L |
| 5.5 mg/dL | 1.78 mmol/L |
| 6.0 mg/dL | 1.94 mmol/L |
| 7.0 mg/dL | 2.26 mmol/L |
| 8.0 mg/dL | 2.58 mmol/L |
Normal Phosphate Levels in mmol/L and mg/dL
| Serum phosphate level | mmol/L | mg/dL |
|---|---|---|
| Normal range, adults | 0.81 – 1.45 | 2.5 – 4.5 |
| Normal range, children (higher while growing) | about 1.3 – 2.3 | about 4.0 – 7.0 |
| Low phosphate (hypophosphatemia) | below 0.81 | below 2.5 |
| Severe hypophosphatemia | below 0.32 | below 1.0 |
| High phosphate (hyperphosphatemia) | above 1.45 | above 4.5 |
Reference ranges vary slightly between laboratories and are higher in children and teenagers. High phosphate is most often caused by chronic kidney disease; low phosphate can follow poor nutrition, alcohol use disorder, refeeding or some medicines. Use the range on your own report and discuss results with your doctor.
Phosphorus to Phosphate Conversion (P to PO4)
Outside blood tests, for example in nutrition, fertiliser or water analysis, results may be given as phosphorus (P) or as the whole phosphate ion (PO4). By weight they differ:
- P to PO4: mg PO4 = mg P × 3.066
- PO4 to P: mg P = mg PO4 × 0.326
- In moles they are equal: 1 mmol P = 1 mmol PO4, so mmol/L values do not change.
Blood phosphate results are already expressed as phosphorus, so you do not need this step to convert a lab report.
Phosphate mmol to mEq
Phosphate carries a mix of charges in the body, so its milliequivalents depend on pH. At normal blood pH (7.4), 1 mmol of phosphate is about 1.8 mEq. Because this varies, phosphate replacement is usually prescribed in mmol, and product labels list both.
Frequently Asked Questions
What is the conversion factor for phosphate mmol/L to mg/dL?
Multiply mmol/L by 3.097 (often rounded to 3.1) to get mg/dL. To go from mg/dL to mmol/L, multiply by 0.3229 (or divide by 3.097).
Are phosphate and phosphorus the same on a lab report?
Yes. Serum phosphate, phosphorus, inorganic phosphate and PO4 all refer to the same blood test and convert with the same factor.
What is 1.4 mmol/L phosphate in mg/dL?
1.4 mmol/L × 3.097 = 4.34 mg/dL, which is in the upper part of the normal adult range.
What is 4.5 mg/dL phosphorus in mmol/L?
4.5 mg/dL ÷ 3.097 = 1.45 mmol/L, the usual upper limit of normal for adults.
What is a normal phosphate level in mmol/L?
For adults, about 0.81–1.45 mmol/L (2.5–4.5 mg/dL). Children have higher normal levels.
How many mg is 1 mmol of phosphorus?
1 mmol of phosphorus weighs 30.97 mg, so 250 mg of phosphorus is about 8 mmol.
How do you convert phosphorus to phosphate?
By weight, multiply phosphorus (P) by 3.066 to get phosphate (PO4). In mmol the two are the same.
Related: calcium mmol/L to mg/dL (phosphate and calcium are often checked together) and all electrolyte and mineral conversions.