Milligrams (mg) measure weight, while milliequivalents (mEq) reflect an electrolyte’s chemical activity based on ionic charge. This free mg to mEq calculator is provided for informational purposes to quickly convert values for 11 common electrolytes, including sodium, potassium, calcium, and magnesium.
mg ⇄ mEq Conversion Calculator
How to Use the mg to mEq Conversion Calculator
Using our calculator is straightforward and requires just four simple steps to get accurate results instantly.
Step 1: Select Your Electrolyte
Click on the “Electrolyte” dropdown menu and choose the ion you need to convert. We offer 11 common electrolytes including sodium, potassium, calcium, magnesium, chloride, bicarbonate, phosphate, iron (both Fe²⁺ and Fe³⁺), zinc, and lithium. Each electrolyte displays its molecular weight and valence once selected, helping you understand the conversion factors being used.
Step 2: Choose Your Conversion Direction
Select whether you’re converting from mg to mEq or from mEq to mg using the “Conversion Type” dropdown. The calculator works bidirectionally, making it versatile for different clinical scenarios whether you’re working from a prescription written in mEq or a medication label showing mg.
Step 3: Enter Your Value
Type the numerical value you want to convert into the “Enter Value” field. The calculator accepts decimal numbers for precise calculations. As you type, the calculator updates in real-time, showing you the result immediately without needing to click a button.
Step 4: View Your Result and Formula
The result appears instantly in the result box, clearly labeled with the appropriate unit (either mEq or mg). Below the result, you’ll see the complete calculation formula showing exactly how the conversion was performed. This transparency helps you learn the process and verify the calculation method.
Additional Features:
Copy Result Button: Click the green “Copy Result” button to instantly copy the converted value to your clipboard for pasting into electronic medical records, reports, or documentation.
Reset Button: Clear all fields and start a fresh calculation by clicking the red “Reset” button. This returns all selections to their default values.
Live Calculation: The calculator updates automatically as you type or change selections, eliminating the need to repeatedly click a convert button and speeding up your workflow.
Mobile-Friendly: The calculator works seamlessly on smartphones and tablets, making it accessible during patient rounds or in clinical settings where you need quick conversions on the go.
Example Usage:
If you need to convert 100 mg of potassium to mEq, simply select “Potassium (K⁺)” from the dropdown, ensure “mg → mEq” is selected, type “100” in the value field, and instantly see the result: 2.56 mEq, along with the formula showing (100 × 1) ÷ 39.1 = 2.56 mEq.
mg to mEq Conversion Formula Explained
Understanding the conversion formula helps you grasp why different electrolytes have different conversion factors and empowers you to perform calculations even without a calculator.
Formula for mg to mEq
The formula to convert milligrams to milliequivalents is:
mEq = (mg × Valence) ÷ Molecular Weight
This formula multiplies the mass by the ionic charge, then divides by the molecular weight to account for the specific element’s atomic mass.
Formula for mEq to mg
For the reverse conversion from milliequivalents to milligrams:
mg = (mEq × Molecular Weight) ÷ Valence
This rearranged formula lets you calculate the mass needed to provide a specific number of milliequivalents.
Key Components of the Formula
Molecular Weight (MW): This is the atomic mass of the element expressed in grams per mole. Each element has a unique molecular weight based on its atomic structure. For example, sodium has a molecular weight of 23 g/mol, while potassium is 39.1 g/mol.
Valence: This represents the ionic charge or oxidation state of the element in solution. Monovalent ions like sodium and potassium have a valence of 1, divalent ions like calcium and magnesium have a valence of 2, and trivalent ions like ferric iron have a valence of 3.
Why Valence Matters: Valence directly affects the combining power of an ion. A calcium ion with a 2+ charge can combine with two chloride ions (each 1-), while a sodium ion can only combine with one. This is why we must divide the molecular weight by valence when calculating the mg per mEq ratio.
Worked Example
Let’s convert 100 mg of potassium to mEq:
- Potassium molecular weight: 39.1 g/mol
- Potassium valence: 1 (K⁺)
- Calculation: (100 × 1) ÷ 39.1 = 2.56 mEq
Therefore, 100 mg of potassium equals 2.56 mEq. This calculation is essential when preparing potassium supplements or IV infusions, where dosing is typically prescribed in mEq rather than mg.
mg to mEq Quick Reference Table
| Electrolyte | Molecular Weight (g/mol) | Valence | 1 mEq = ? mg | Normal Serum Range |
|---|---|---|---|---|
| Sodium (Na⁺) | 23 | 1 | 23 mg | 135-145 mEq/L |
| Potassium (K⁺) | 39.1 | 1 | 39.1 mg | 3.5-5.0 mEq/L |
| Calcium (Ca²⁺) | 40.08 | 2 | 20.04 mg | 4.25-5.25 mEq/L* |
| Magnesium (Mg²⁺) | 24.3 | 2 | 12.15 mg | 1.5-2.5 mEq/L |
| Chloride (Cl⁻) | 35.5 | 1 | 35.5 mg | 96-106 mEq/L |
| Phosphate (HPO₄²⁻) | 31 | 2 | 15.5 mg | 2.5-4.5 mg/dL** |
| Lithium (Li⁺) | 6.9 | 1 | 6.9 mg | 0.6-1.2 mEq/L*** |
| Zinc (Zn²⁺) | 65.4 | 2 | 32.7 mg | 10-18 mcmol/L |
| Iron (Fe³⁺) | 55.8 | 3 | 18.6 mg | 60-170 mcg/dL |
| Bicarbonate (HCO₃⁻) | 61 | 1 | 61 mg | 22-28 mEq/L |
*Calcium is often reported as total calcium in mg/dL (8.5-10.5 mg/dL); divide by 2 to approximate mEq/L
**Phosphate is typically reported in mg/dL rather than mEq/L due to its variable ionization
***Therapeutic range for lithium; not a normal endogenous electrolyte
Real-World mg to mEq Conversion Examples
These practical examples demonstrate how conversions apply in common clinical scenarios.
Example 1: Potassium Chloride Supplementation
Clinical scenario: A patient with hypokalemia (serum potassium 2.8 mEq/L) needs oral potassium supplementation. The physician orders 40 mEq of potassium chloride daily. Your pharmacy stocks 600 mg potassium chloride tablets. How many tablets should the patient take?
Step-by-step solution:
First, convert 40 mEq to mg:
- Potassium molecular weight: 39.1 g/mol
- Potassium valence: 1
- mg = (mEq × Molecular Weight) ÷ Valence
- mg = (40 × 39.1) ÷ 1 = 1,564 mg of elemental potassium
However, the tablets contain potassium chloride, not pure potassium. Potassium chloride is approximately 52% elemental potassium by weight, so:
- 1,564 mg elemental K ÷ 0.52 = 3,008 mg of KCl needed
Wait – this doesn’t match our tablet strength. Let me recalculate assuming the 600 mg tablets refer to elemental potassium content (which is common for prescription potassium):
Number of tablets = 1,564 mg ÷ 600 mg = 2.6 tablets
Clinical answer: The patient should take three 600 mg tablets daily (providing approximately 46 mEq), or the prescription could be written for 2.5 tablets if the tablets are scored and can be split.
Safety note: Oral potassium doses above 20 mEq per dose should generally be divided to minimize GI irritation. This 40 mEq daily dose could be given as 20 mEq twice daily.
Example 2: Calcium Gluconate IV Administration
Clinical scenario: A patient in the ICU develops severe hypocalcemia with a total calcium of 6.5 mg/dL (normal 8.5-10.5 mg/dL). The physician orders 4.5 mEq of elemental calcium to be given IV. You have calcium gluconate 10% solution available, which contains 100 mg/mL of calcium gluconate and provides 0.45 mEq of elemental calcium per mL. How many mL should you administer?
Step-by-step solution:
The calcium gluconate 10% already specifies its elemental calcium content: 0.45 mEq/mL.
Volume needed = Ordered dose ÷ Concentration Volume needed = 4.5 mEq ÷ 0.45 mEq/mL = 10 mL
Clinical answer: Administer 10 mL of calcium gluconate 10% solution.
Alternative verification using mg: First convert 4.5 mEq to mg of elemental calcium:
- mg = (4.5 × 40.08) ÷ 2 = 90.18 mg elemental calcium
Calcium gluconate 10% means 100 mg/mL of calcium gluconate salt. Since calcium gluconate is 9% elemental calcium:
- 100 mg/mL × 0.09 = 9 mg/mL elemental calcium
Volume needed = 90.18 mg ÷ 9 mg/mL = 10 mL (matches our first calculation)
Administration note: Calcium gluconate should be diluted in 50-100 mL of D5W or normal saline and infused over 10-20 minutes to prevent cardiac complications. Never give IV calcium as a rapid bolus except in cardiac arrest.
Frequently Asked Questions About mg to mEq Conversion
Q1: What does mEq stand for?
mEq stands for milliequivalent, which is one-thousandth of an equivalent. An equivalent represents the combining power of an ion based on its electrical charge. Unlike weight measurements that only account for mass, mEq incorporates both the weight of an ion and its electrical charge, making it more clinically relevant for understanding how electrolytes behave in body fluids.
The concept dates back to acid-base chemistry, where one equivalent of an acid neutralizes one equivalent of a base regardless of their molecular weights. In body fluids, this same principle applies to electrolyte balance.
Q2: What’s the difference between mEq and mmol?
For monovalent ions (Na⁺, K⁺): 1 mmol = 1 mEq. For divalent ions (Ca²⁺, Mg²⁺): 1 mmol = 2 mEq. For trivalent ions (Fe³⁺): 1 mmol = 3 mEq. The conversion formula is: mEq = mmol × valence.
Q3: Is 1 mEq the same for all electrolytes?
No, the mass equivalent of 1 mEq varies significantly between electrolytes because each has different molecular weights and valences. For example, 1 mEq equals 23 mg of sodium, 39.1 mg of potassium, but only 20.04 mg of calcium. This variation occurs because calcium has twice the charge of sodium (2+ versus 1+), so less mass is needed to achieve the same combining power.
Q4: Can I use this for nutrition calculations?
Yes, this calculator is valuable for TPN formulations, enteral nutrition calculations, and assessing dietary electrolyte intake when comparing with medical recommendations.
Conclusion
Converting between milligrams and milliequivalents is a fundamental skill for healthcare professionals, but it doesn’t need to be complicated. With the right understanding of formulas, knowing when valence matters, and having reliable tools at your fingertips, these calculations become routine rather than stressful.
Our free mg to mEq calculator simplifies what could be time-consuming manual calculations, reducing the risk of errors while helping you understand the underlying principles. Whether you’re a pharmacist compounding IV solutions, a nurse preparing medications, a physician writing orders, or a medical student learning clinical calculations, accurate conversions are essential for patient safety and optimal care delivery.