How to Use the mg to mEq Conversion Calculator
Milligrams measure weight, while milliequivalents reflect an ion's chemical activity based on charge. This calculator converts values for common electrolytes using molecular weight and valence.
Step 1: Select the electrolyte from the dropdown menu. Each option uses its own molecular weight and valence.
Step 2: Choose the conversion direction: mg to mEq or mEq to mg. The calculator works both ways.
Step 3: Enter your value. The result updates instantly and shows the formula used for transparency.
Step 4: Copy the result if you need it for notes, documentation, or study materials.
mg to mEq Conversion Formula Explained
The formula to convert milligrams to milliequivalents is:
mEq = (mg x valence) / molecular weight For the reverse conversion from milliequivalents to milligrams:
mg = (mEq x molecular weight) / valence Molecular weight is the atomic or formula mass in grams per mole. Valence is the ionic charge. Monovalent ions like sodium and potassium have a valence of 1, while divalent ions like calcium and magnesium have a valence of 2.
Worked Example
To convert 100 mg of potassium to mEq, use potassium's molecular weight of 39.1 g/mol and valence of 1.
(100 x 1) / 39.1 = 2.56 mEq Therefore, 100 mg of elemental potassium equals approximately 2.56 mEq.
Potassium mg to mEq Conversion Table
Potassium is the most common reason people convert mg to mEq, usually from a supplement label. For elemental potassium, divide the milligram amount by 39.1. These are the values most often searched:
| Elemental potassium (mg) | mEq | Context |
|---|---|---|
| 90 mg | 2.30 mEq | Low-dose supplement |
| 99 mg | 2.53 mEq | Standard OTC potassium tablet (elemental) |
| 200 mg | 5.12 mEq | Combined daily supplement |
| 280 mg | 7.16 mEq | Higher-dose supplement |
| 422 mg | 10.79 mEq | Common label amount (per serving) |
| 600 mg | 15.35 mEq | High-dose elemental potassium |
Potassium chloride (KCl) is different. Supplement and prescription labels often list the potassium chloride salt, which has a molecular weight of about 74.55. Divide the KCl milligram amount by 74.55 to get mEq:
| Potassium chloride (mg) | mEq | Typical label |
|---|---|---|
| 600 mg | 8.05 mEq | Often labeled ~8 mEq |
| 750 mg | 10.06 mEq | Often labeled 10 mEq (e.g. SR tablets) |
| 1500 mg | 20.12 mEq | Often labeled 20 mEq |
Always check whether your label lists elemental potassium or a potassium salt before converting, because the two give different mEq values.
mEq to mg Conversion (Reverse)
To go the other way, multiply mEq by the molecular weight and divide by valence. For elemental potassium that means mg = mEq x 39.1, so 10 mEq is about 391 mg and 20 mEq is about 782 mg. Switch the calculator to the mEq to mg direction to do this automatically for any electrolyte.
mg to mEq Quick Reference Table
Use this table as a quick reference for common electrolytes. The value for 1 mEq in mg is molecular weight divided by valence.
| Electrolyte | Molecular weight | Valence | 1 mEq equals | Common range/context |
|---|---|---|---|---|
| Potassium (K+) | 39.1 g/mol | 1 | 39.1 mg | 3.5-5.0 mEq/L |
| Sodium (Na+) | 23 g/mol | 1 | 23 mg | 135-145 mEq/L |
| Calcium (Ca2+) | 40.08 g/mol | 2 | 20.04 mg | 4.25-5.25 mEq/L |
| Magnesium (Mg2+) | 24.3 g/mol | 2 | 12.15 mg | 1.5-2.5 mEq/L |
| Chloride (Cl-) | 35.5 g/mol | 1 | 35.5 mg | 96-106 mEq/L |
| Bicarbonate (HCO3-) | 61 g/mol | 1 | 61 mg | 22-28 mEq/L |
| Phosphate (HPO4 2-) | 31 g/mol | 2 | 15.5 mg | Often reported in mg/dL |
| Iron (Fe2+) | 55.8 g/mol | 2 | 27.9 mg | Varies by test |
| Iron (Fe3+) | 55.8 g/mol | 3 | 18.6 mg | 60-170 mcg/dL |
| Zinc (Zn2+) | 65.4 g/mol | 2 | 32.7 mg | 10-18 µmol/L |
| Lithium (Li+) | 6.9 g/mol | 1 | 6.9 mg | 0.6-1.2 mEq/L |
Calcium is often reported as total calcium in mg/dL, phosphate is often reported in mg/dL because ionization can vary, and lithium values refer to therapeutic monitoring rather than an endogenous electrolyte range.
Why Valence Matters
Valence represents the charge or combining power of an ion. A sodium ion carries one positive charge, so 1 mmol of sodium equals 1 mEq. Calcium carries two positive charges, so the same mole amount contributes twice the equivalent charge.
This is why 1 mEq is not the same mass for every electrolyte. 1 mEq of sodium is 23 mg, 1 mEq of potassium is 39.1 mg, and 1 mEq of calcium is about 20.04 mg.
Real-World Conversion Examples
Potassium Conversion
If you need to convert elemental potassium from mg to mEq, select potassium and use the mg to mEq direction. For 100 mg potassium, the result is about 2.56 mEq.
Calcium Conversion
Calcium has a molecular weight of 40.08 and valence of 2. A 90 mg elemental calcium value converts to about 4.49 mEq. For serum calcium values in mg/dL, mmol/L, and mEq/L, use the Calcium Conversion Calculator.
Magnesium Conversion
Magnesium has a molecular weight of 24.3 and valence of 2. A 24.3 mg elemental magnesium value converts to 2 mEq.
Important Safety Notes
This calculator converts elemental ion amounts only. Medication salts and supplement labels may list compound weights, not elemental amounts. For example, potassium chloride weight is not the same as elemental potassium weight.
Do not use this calculator by itself to determine medication doses, infusion amounts, or treatment decisions. Always follow institutional protocols and verify with a qualified healthcare professional.
Frequently Asked Questions
What does mEq stand for?
mEq stands for milliequivalent, one-thousandth of an equivalent. It reflects the combining power of an ion based on its electrical charge.
What is the difference between mEq and mmol?
For monovalent ions, 1 mmol equals 1 mEq. For divalent ions, 1 mmol equals 2 mEq. The formula is mEq = mmol x valence, which is the same valence logic used in the mmol/L to mEq/L Conversion Calculator.
Is 1 mEq the same for all electrolytes?
No. The mass of 1 mEq varies because electrolytes have different molecular weights and valences.
Can I use this for nutrition calculations?
This calculator can help with educational comparison of elemental electrolyte units, but nutrition or clinical dosing calculations should be confirmed with appropriate professional guidance.
Conclusion
Converting between milligrams and milliequivalents is easier when you know the molecular weight and valence. The calculator performs the arithmetic instantly and shows the formula so you can verify the method.
Use it for learning, documentation support, and unit comparison, while keeping medical decisions anchored to clinical judgment and verified protocols.