Converting electrolyte values between mEq/L and mmol/L is a common challenge for medical technicians & students worldwide. Our free mEq/L to mmol/L conversion calculator provides instant, accurate conversions for sodium, potassium, calcium, magnesium, and other essential electrolytes.
mEq/L ⇄ mmol/L Conversion Calculator
Understanding mEq/L and mmol/L
Milliequivalents per liter (mEq/L) is a unit of measurement that represents the chemical combining power of an electrolyte. Unlike standard concentration units, mEq/L takes into account both the concentration and the electrical charge (valence) of ions in solution.
In medical settings, mEq/L is commonly used in the United States and some other countries to express electrolyte concentrations in blood, urine, and other body fluids. This unit is particularly useful for substances that carry electrical charges, such as sodium, potassium, chloride, calcium, and magnesium.
Common substances measured in mEq/L include:
- Sodium (Na⁺) – the primary extracellular cation
- Potassium (K⁺) – the primary intracellular cation
- Chloride (Cl⁻) – a major extracellular anion
- Bicarbonate (HCO₃⁻) – important for acid-base balance
- Calcium (Ca²⁺) – essential for muscle and nerve function
- Magnesium (Mg²⁺) – crucial for enzymatic reactions
Millimoles per liter (mmol/L) is the International System of Units (SI) standard for measuring substance concentration. One millimole represents one-thousandth of a mole, which is based on Avogadro’s number of particles.
The mmol/L unit is preferred in most countries worldwide, including Europe, Canada, Australia, and many Asian nations. International medical journals and research publications typically report electrolyte values in mmol/L to maintain global consistency.
This standardized measurement system facilitates international collaboration, makes research more reproducible, and reduces confusion when healthcare providers work across borders or interpret studies from different countries.
How to Convert mEq/L to mmol/L
The Basic Formula
The conversion from mEq/L to mmol/L depends on one crucial factor: the valence (electrical charge) of the ion. The formula is straightforward:
mmol/L = mEq/L ÷ Valence
The valence represents the number of charges an ion carries. For example:
- Monovalent ions (one charge) like Na⁺, K⁺, and Cl⁻ have a valence of 1
- Divalent ions (two charges) like Ca²⁺ and Mg²⁺ have a valence of 2
- Trivalent ions (three charges) like PO₄³⁻ have a valence of 3
Example with Potassium (K⁺): If a lab report shows potassium at 4.5 mEq/L:
- Valence of potassium = 1
- Calculation: 4.5 ÷ 1 = 4.5 mmol/L
- Result: 4.5 mEq/L = 4.5 mmol/L
For monovalent ions, the values are identical because dividing by 1 doesn’t change the number.
Example with Calcium (Ca²⁺): If a lab report shows calcium at 5.0 mEq/L:
- Valence of calcium = 2
- Calculation: 5.0 ÷ 2 = 2.5 mmol/L
- Result: 5.0 mEq/L = 2.5 mmol/L
Step-by-Step Conversion Process
Follow these four simple steps for accurate conversion:
Step 1: Identify the Substance/Electrolyte Determine exactly which electrolyte you’re converting. Is it sodium, potassium, calcium, magnesium, or another ion? This is crucial because different electrolytes have different valences.
Step 2: Determine the Valence Look up the valence of the ion. Refer to the valence chart below or use our calculator’s automatic valence detection. Remember:
- Most common electrolytes (Na⁺, K⁺, Cl⁻) have valence = 1
- Calcium and magnesium have valence = 2
- Phosphate has valence = 3
Step 3: Apply the Formula Divide the mEq/L value by the valence number. Use a calculator for precision, especially with divalent and trivalent ions where decimal accuracy matters.
Step 4: Verify Your Result Double-check your calculation, especially for clinical decisions. Compare your result against normal reference ranges to ensure the answer makes physiological sense.
Valence Chart for Common Electrolytes
| Electrolyte | Chemical Symbol | Valence | mEq/L to mmol/L | mmol/L to mEq/L |
|---|---|---|---|---|
| Sodium | Na⁺ | 1 | Divide by 1 | Multiply by 1 |
| Potassium | K⁺ | 1 | Divide by 1 | Multiply by 1 |
| Chloride | Cl⁻ | 1 | Divide by 1 | Multiply by 1 |
| Calcium | Ca²⁺ | 2 | Divide by 2 | Multiply by 2 |
| Magnesium | Mg²⁺ | 2 | Divide by 2 | Multiply by 2 |
| Bicarbonate | HCO₃⁻ | 1 | Divide by 1 | Multiply by 1 |
| Phosphate | PO₄³⁻ | 3 | Divide by 3 | Multiply by 3 |
Quick Reference Guide:
- If converting a monovalent ion (Na⁺, K⁺, Cl⁻, HCO₃⁻), the number stays the same
- If converting a divalent ion (Ca²⁺, Mg²⁺), divide by 2 for mEq/L→mmol/L or multiply by 2 for mmol/L→mEq/L
- If converting a trivalent ion (PO₄³⁻), divide by 3 for mEq/L→mmol/L or multiply by 3 for mmol/L→mEq/L
Common Electrolyte Conversions
Sodium (Na⁺) Conversion
Normal Range: 135-145 mEq/L = 135-145 mmol/L
Sodium is the most abundant cation in extracellular fluid and plays a vital role in maintaining fluid balance, blood pressure, and nerve impulse transmission. Because sodium has a valence of 1, conversions are straightforward—the values remain identical.
Example Conversions:
- 138 mEq/L = 138 mmol/L (normal)
- 130 mEq/L = 130 mmol/L (hyponatremia)
- 150 mEq/L = 150 mmol/L (hypernatremia)
Clinical Significance: Sodium imbalances can cause serious neurological symptoms. Hyponatremia (low sodium) may lead to confusion, seizures, or coma, while hypernatremia (high sodium) can cause dehydration and altered mental status.
Potassium (K⁺) Conversion
Normal Range: 3.5-5.0 mEq/L = 3.5-5.0 mmol/L
Potassium is the primary intracellular cation and is critical for cardiac function, muscle contraction, and nerve transmission. Like sodium, potassium has a valence of 1, making conversions simple.
Example Conversions:
- 4.2 mEq/L = 4.2 mmol/L (normal)
- 3.0 mEq/L = 3.0 mmol/L (hypokalemia)
- 6.0 mEq/L = 6.0 mmol/L (hyperkalemia)
Clinical Significance: Potassium monitoring is critical because both high and low levels can cause life-threatening cardiac arrhythmias. Even small changes can have significant clinical implications, making accurate measurement and conversion essential.
Calcium (Ca²⁺) Conversion
Normal Range: 4.5-5.5 mEq/L = 2.25-2.75 mmol/L
Calcium is essential for bone health, muscle contraction, blood clotting, and nerve function. With a valence of 2, calcium conversions require careful calculation.
Example Conversions:
- 5.0 mEq/L ÷ 2 = 2.5 mmol/L (normal)
- 4.0 mEq/L ÷ 2 = 2.0 mmol/L (hypocalcemia)
- 6.0 mEq/L ÷ 2 = 3.0 mmol/L (hypercalcemia)
Reverse Conversions:
- 2.5 mmol/L × 2 = 5.0 mEq/L (normal)
- 2.0 mmol/L × 2 = 4.0 mEq/L (hypocalcemia)
- 3.0 mmol/L × 2 = 6.0 mEq/L (hypercalcemia)
Clinical Significance: Calcium abnormalities affect multiple organ systems. Hypocalcemia can cause tetany, seizures, and cardiac dysfunction, while hypercalcemia may lead to kidney stones, confusion, and cardiac arrhythmias.
Magnesium (Mg²⁺) Conversion
Normal Range: 1.5-2.5 mEq/L = 0.75-1.25 mmol/L
Magnesium is involved in over 300 enzymatic reactions, including energy production, protein synthesis, and muscle/nerve function. As a divalent cation, magnesium requires the same conversion factor as calcium.
Example Conversions:
- 2.0 mEq/L ÷ 2 = 1.0 mmol/L (normal)
- 1.2 mEq/L ÷ 2 = 0.6 mmol/L (hypomagnesemia)
- 3.0 mEq/L ÷ 2 = 1.5 mmol/L (hypermagnesemia)
Reverse Conversions:
- 1.0 mmol/L × 2 = 2.0 mEq/L (normal)
- 0.6 mmol/L × 2 = 1.2 mEq/L (hypomagnesemia)
- 1.5 mmol/L × 2 = 3.0 mEq/L (hypermagnesemia)
Clinical Significance: Magnesium deficiency is common in hospitalized patients and can cause muscle cramps, cardiac arrhythmias, and potassium depletion. Hypermagnesemia is less common but can impair neuromuscular transmission.
Conversion Examples & Practice Problems
Example 1: Converting Sodium
Problem: A patient’s lab report from a European hospital shows sodium at 140 mmol/L. Convert this to mEq/L for your US-based medical record.
Solution:
- Identify the substance: Sodium (Na⁺)
- Determine the valence: 1
- Apply the formula: mEq/L = mmol/L × Valence
- Calculate: 140 × 1 = 140
- Answer: 140 mEq/L
Interpretation: This is within the normal range (135-145 mEq/L), indicating normal sodium balance.
Example 2: Converting Calcium
Problem: A patient has serum calcium of 2.5 mmol/L. Convert this value to mEq/L.
Solution:
- Identify the substance: Calcium (Ca²⁺)
- Determine the valence: 2
- Apply the formula: mEq/L = mmol/L × Valence
- Calculate: 2.5 × 2 = 5.0
- Answer: 5.0 mEq/L
Interpretation: This is within the normal range (4.5-5.5 mEq/L), indicating normal calcium status.
Example 3: Converting Magnesium
Problem: A critical care protocol lists a magnesium target of 4 mEq/L. Convert this to mmol/L for ordering from a pharmacy that uses SI units.
Solution:
- Identify the substance: Magnesium (Mg²⁺)
- Determine the valence: 2
- Apply the formula: mmol/L = mEq/L ÷ Valence
- Calculate: 4 ÷ 2 = 2.0
- Answer: 2.0 mmol/L
Interpretation: This target is at the upper end of normal (0.75-1.25 mmol/L), appropriate for a patient receiving aggressive magnesium replacement.
Example 4: Converting Potassium
Problem: A research paper reports that hyperkalemia was defined as potassium >5.5 mmol/L. What is this cutoff in mEq/L?
Solution:
- Identify the substance: Potassium (K⁺)
- Determine the valence: 1
- Apply the formula: mEq/L = mmol/L × Valence
- Calculate: 5.5 × 1 = 5.5
- Answer: 5.5 mEq/L
Interpretation: This matches the typical US definition of hyperkalemia, confirming the universal nature of this clinical threshold.
Normal Electrolyte Ranges
| Electrolyte | Normal Range (mEq/L) | Normal Range (mmol/L) | Clinical Notes |
|---|---|---|---|
| Sodium | 135-145 | 135-145 | Most abundant extracellular cation |
| Potassium | 3.5-5.0 | 3.5-5.0 | Critical for cardiac function |
| Chloride | 96-106 | 96-106 | Major extracellular anion |
| Calcium | 4.5-5.5 | 2.25-2.75 | Essential for multiple functions |
| Magnesium | 1.5-2.5 | 0.75-1.25 | Cofactor in 300+ reactions |
| Bicarbonate | 22-28 | 22-28 | Primary buffer system |
| Phosphate | 2.5-4.5 | 0.81-1.45 | Bone health and energy metabolism |
Important Notes:
- Reference ranges may vary slightly between laboratories based on methodology and population
- Always use your institution’s specific reference ranges when available
- Pediatric ranges differ from adult ranges
- Some conditions require tighter therapeutic ranges than standard reference intervals
- Total calcium vs ionized calcium have different ranges (values above represent total calcium)
Tips for Using the Calculator
Select the Correct Substance First: The calculator automatically applies the correct valence when you choose the substance. Always verify you’ve selected the right electrolyte before entering values.
Choose Your Conversion Direction: Clearly indicate whether you’re converting from mEq/L to mmol/L or vice versa. The calculator handles both directions seamlessly.
Enter Accurate Values: Input your values carefully, including decimal places. For clinical use, precision matters—especially for electrolytes with narrow therapeutic ranges like potassium.
Double-Check Results for Critical Decisions: While the calculator is accurate, always verify results when making critical clinical decisions, especially for medication dosing or treatment protocols.
Use the Copy Function: The built-in copy button allows you to easily transfer results to electronic health records, documents, or notes without transcription errors.
Bookmark for Future Use: Save this page for quick access whenever you need electrolyte conversions. Mobile-friendly design means you can use it anywhere.
Understand the Valence: Take a moment to understand why different electrolytes convert differently. This knowledge will help you catch potential errors and strengthen your clinical understanding.
Conclusion
Understanding how to convert between mEq/L and mmol/L is an essential skill for modern healthcare professionals. Whether you’re interpreting international research, managing patient transfers, or simply working in a globalized medical environment, accurate electrolyte conversion ensures patient safety and optimal care.
Our mEq/L to mmol/L conversion calculator eliminates the guesswork and reduces the risk of calculation errors. With automatic valence detection and instant results, you can focus on clinical decision-making rather than arithmetic. The tool supports all common electrolytes including sodium, potassium, calcium, magnesium, chloride, bicarbonate, and phosphate.
Remember that while conversions are mathematically straightforward, clinical interpretation requires considering the patient’s overall condition, other laboratory values, and clinical presentation. This calculator provides accurate conversions, but professional judgment remains paramount in patient care.
Bookmark this page and share it with colleagues who might benefit from quick, reliable electrolyte conversions. For questions, feedback, or suggestions for additional calculators, please contact us through the website.
Medical Disclaimer: This calculator and the information provided are for educational and informational purposes only. They are not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of information obtained from this calculator. The accuracy of conversions should be verified for critical clinical decisions, and institutional protocols should always be followed.