mEq to mg Calculator
Convert between milliequivalents (mEq) and milligrams (mg) for ions
How It Works
This calculator converts between milliequivalents (mEq) and milligrams (mg) using the following formulas:
To convert mEq to mg:
mg = (mEq × Atomic Weight) / Valence
To convert mg to mEq:
mEq = (mg × Valence) / Atomic Weight
Perfect for healthcare professionals, pharmacists, chemists, and students working with electrolyte calculations and pharmaceutical dosing.
Data Sources
- • IUPAC Technical Report 2021 (DOI: 10.1515/pac-2019-0603)
- • NIST Chemistry WebBook (SRD 69)
- • Standard atomic weights from the International Union of Pure and Applied Chemistry
Letters to Numbers
Trusted Conversion Tools
mEq to mg Calculator
Convert milliequivalents (mEq) to milligrams (mg) — and mg back to mEq — for potassium, sodium, calcium, magnesium, chloride, and more. Select the ion, enter the value, and get an instant result with the formula shown. Essential for medication dosing, electrolyte calculations, and pharmaceutical reference.
How It Works
Use the interactive tool on the left to encode, decode, or solve your input. The tool provides real-time results as you type or make selections.
Features
- Real-time processing with instant results
- Works completely offline - no data sent to servers
- Copy results to clipboard easily
- Free and always available
Other Tools
Explore more tools by clicking the + button above
Your Privacy Matters
All processing happens in your browser. We never store, send, or log your data. Completely private and secure.
mEq vs mg — What's the Difference?
mg (milligrams) measures mass — how much of a substance there is by weight. mEq (milliequivalents) measures chemical combining capacity — it accounts for both the mass and the ionic charge (valence) of the substance. This distinction matters enormously in medicine and pharmacy, where the physiological effect of an electrolyte depends on the number of charges it carries, not just its mass.
mg (milligrams)
- • Measures mass
- • Universal unit for any substance
- • Does not reflect ionic charge
- • Used in supplement labels, food nutrition
mEq (milliequivalents)
- • Measures chemical equivalents (mass × charge)
- • Ion-specific — different for each electrolyte
- • Reflects physiological activity
- • Used in IV solutions, electrolyte prescriptions
In clinical practice, electrolytes are often ordered in mEq (e.g., "give 40 mEq potassium IV") because the unit reflects biological activity. Supplement labels often use mg. The mEq to mg conversion bridges these two systems.
The mEq to mg Formula
The conversion between milliequivalents and milligrams uses atomic weight and valence:
mEq → mg
mg = mEq × (atomic weight ÷ valence)
mg → mEq
mEq = mg ÷ (atomic weight ÷ valence)
Equivalent weight (shorthand)
Equivalent weight = atomic weight ÷ valence
1 mEq of any ion = its equivalent weight in mg
Example: 10 mEq potassium to mg
Potassium: atomic weight = 39.1, valence = 1
Equivalent weight = 39.1 ÷ 1 = 39.1 mg/mEq
10 mEq × 39.1 = 391 mg
mEq to mg Conversion — Electrolyte Reference Table
The table below shows the equivalent weight for each common electrolyte — that is, how many milligrams equal 1 mEq. Use it to convert any mEq value to mg by multiplying, or any mg value to mEq by dividing.
| Ion | Atomic Weight | Valence | 1 mEq = X mg | 1 mg = X mEq |
|---|---|---|---|---|
| Potassium (K⁺) | 39.1 | 1 | 39.1 mg | 0.0256 mEq |
| Sodium (Na⁺) | 22.99 | 1 | 22.99 mg | 0.0435 mEq |
| Calcium (Ca²⁺) | 40.08 | 2 | 20.04 mg | 0.0499 mEq |
| Magnesium (Mg²⁺) | 24.31 | 2 | 12.16 mg | 0.0822 mEq |
| Chloride (Cl⁻) | 35.45 | 1 | 35.45 mg | 0.0282 mEq |
| Bicarbonate (HCO₃⁻) | 61.02 | 1 | 61.02 mg | 0.0164 mEq |
| Phosphate (HPO₄²⁻) | 96 | 2 | 48 mg | 0.0208 mEq |
Atomic weights sourced from IUPAC 2021 standard atomic weights. Values rounded to 2 decimal places.
mEq to mg Potassium — Quick Reference Table
Potassium is by far the most commonly looked-up electrolyte for mEq to mg conversion — it's ordered in mEq in IV and oral supplementation but listed in mg on supplement labels. The table covers the most searched values: 2 mEq potassium to mg, 10 mEq to mg, and 25 mEq potassium to mg.
| Potassium (mEq) | Potassium (mg) | Clinical context |
|---|---|---|
| 1 mEq | 39.1 mg | Single tablet reference |
| 2 mEq | 78.2 mg | 2 mEq KCl tablet (common oral dose) |
| 5 mEq | 195.5 mg | Small IV supplement |
| 10 mEq | 391 mg | 10 mEq KCl — frequent oral supplement dose |
| 20 mEq | 782 mg | Daily oral potassium supplement |
| 25 mEq | 977.5 mg | 25 mEq — typical IV bag additive |
| 40 mEq | 1564 mg | 40 mEq KCl — standard IV repletion bag |
| 50 mEq | 1955 mg | High-dose IV potassium replacement |
| 100 mEq | 3910 mg | Full daily dietary potassium reference |
Formula: mg = mEq × 39.1 (potassium equivalent weight). Values rounded to 1 decimal place.
mEq to mg for Sodium, Calcium, and Magnesium
Sodium (Na⁺)
1 mEq = 22.99 mg
| mEq | mg |
|---|---|
| 1 | 23 |
| 10 | 230 |
| 20 | 460 |
| 40 | 920 |
| 154 | 3540 |
154 mEq/L is normal saline concentration
Calcium (Ca²⁺)
1 mEq = 20.04 mg
| mEq | mg |
|---|---|
| 1 | 20 |
| 4.5 | 90.2 |
| 9 | 180.4 |
| 10 | 200.4 |
Normal serum calcium ≈ 4.5–5.5 mEq/L
Magnesium (Mg²⁺)
1 mEq = 12.16 mg
| mEq | mg |
|---|---|
| 1 | 12.2 |
| 2 | 24.3 |
| 4 | 48.6 |
| 8 | 97.2 |
Normal serum magnesium ≈ 1.8–2.2 mEq/L
When Is mEq Used vs mg?
IV solutions and electrolyte orders
Hospital pharmacies and physicians order electrolyte supplements in mEq because the unit reflects physiological equivalence. "40 mEq KCl in 1L NS" means 40 milliequivalents of potassium chloride — a clinically meaningful quantity.
Oral prescription medications
Prescription potassium tablets (e.g. KCl extended-release) are dosed in mEq. Over-the-counter potassium supplements are limited to 99 mg per tablet in the US, so the label typically shows mg.
Laboratory results and serum levels
Serum electrolyte panels report in mEq/L (or mmol/L for monovalent ions, which are numerically equal). Normal serum potassium is 3.5–5.0 mEq/L.
Food and supplement labels
Supplement labels and food nutrition panels use mg. A banana contains roughly 422 mg of potassium — about 10.8 mEq.
Pharmacy compounding and IV admixture
When compounding IV solutions, pharmacists work in mEq. Converting a physician's mEq order to mg (or vice versa) is one of the most common pharmaceutical calculations.
Frequently Asked Questions
How do you convert mEq to mg?
Multiply the mEq value by the ion's equivalent weight (atomic weight ÷ valence). For potassium: mg = mEq × 39.1. For sodium: mg = mEq × 23. For calcium: mg = mEq × 20.04. For magnesium: mg = mEq × 12.16.
How many mg is 10 mEq of potassium?
10 mEq of potassium = 391 mg. (10 × 39.1 mg/mEq = 391 mg)
How many mg is 2 mEq of potassium?
2 mEq of potassium = 78.2 mg. (2 × 39.1 = 78.2 mg)
How many mg is 25 mEq of potassium?
25 mEq of potassium = 977.5 mg (approximately 978 mg). (25 × 39.1 = 977.5 mg)
What is the difference between mEq and mg?
mg measures mass. mEq (milliequivalents) measures chemical combining capacity — it accounts for both mass and ionic charge (valence). For monovalent ions (like Na⁺, K⁺), 1 mEq = atomic weight in mg. For divalent ions (Ca²⁺, Mg²⁺), 1 mEq = half the atomic weight in mg.
How do you convert mg to mEq for potassium?
Divide the mg value by 39.1 (potassium's equivalent weight). Example: 391 mg ÷ 39.1 = 10 mEq potassium.
Disclaimer: This calculator is provided for educational and reference purposes. Always verify medication calculations with a licensed pharmacist or healthcare provider before clinical use. Do not make medical decisions based solely on this tool.