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mEq to Milligrams (mg) — Medical Calculator

Use this free mEq to mg converter to instantly convert milliequivalents to milligrams — and back. Supports 7 common medical ions including sodium, potassium, calcium, and magnesium. Includes step-by-step calculation for nurses, pharmacists, and students.

mEq → mg & mg → mEq
7 ions — Na, K, Ca, Mg, Cl & more
Step-by-step solution shown
Manual mode for custom ions
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mEq to mg Converter

Convert milliequivalents to milligrams — or reverse — using ion-specific molecular weight and valency.

mEq
g/mol
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Please enter a value and select an ion (or enable manual mode).
Result
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📋 Step-by-Step Calculation

Important Medical Disclaimer

→ This mEq to mg converter is intended for educational and informational purposes only.

→ Always verify electrolyte and medication doses with a licensed healthcare professional or pharmacist before clinical use.

→ Molecular weight and valency values used in this milliequivalent calculator are based on standard reference data. Minor variations may exist across sources.

→ Sources: igcsepro.org, caesarcipher.org, IUPAC Technical Report 2021, NIST Chemistry WebBook (SRD 69), National Institutes of Health (NIH)

What is mEq? A Simple Medical Explanation

mEq stands for milliequivalent — a unit of measurement used in medicine and chemistry to express the chemical activity of an ion in a solution. Unlike milligrams, which measure mass alone, milliequivalents account for both the mass of an ion and its electrical charge (valency). This makes mEq particularly useful in clinical medicine where the ionic activity of electrolytes matters more than their raw weight.

One milliequivalent is one thousandth of an equivalent. An equivalent is defined as the amount of a substance that reacts with or replaces one mole of hydrogen ions. For ions with a valency of 1 (such as sodium or potassium), 1 mEq equals 1 millimole. For divalent ions like calcium or magnesium (valency 2), 1 mEq equals 0.5 millimoles.

This mEq to mg converter uses the standard milliequivalent calculator formula to perform instant, accurate conversions for the most common medical ions.

mEq to mg Formula — How the Calculation Works

The mEq to mg converter uses two core formulas depending on the direction of conversion. Both require the molecular weight and valency of the ion being converted.

mg = (mEq × Molecular Weight) ÷ Valency

Use this formula to convert milliequivalents to milligrams.

mEq = (mg × Valency) ÷ Molecular Weight

Use this formula for the mg to mEq calculator direction.

Why valency matters

Valency is the number of electrons an ion can donate or accept — essentially its electrical charge. Sodium (Na⁺) has a valency of 1, while calcium (Ca²⁺) has a valency of 2. A higher valency means that fewer milligrams are needed to produce the same number of milliequivalents, which is why divalent ions like calcium require the valency to be factored into the milliequivalent calculator formula.

Step-by-Step Example — mEq to mg Conversion

Example 1: Potassium (K⁺) — 20 mEq to mg

  • Given: 20 mEq of Potassium (K⁺)
  • Molecular weight of K: 39.1 g/mol
  • Valency of K⁺: 1
  • Formula: mg = (mEq × MW) ÷ valency
  • Calculation: (20 × 39.1) ÷ 1 = 782 mg

Example 2: Calcium (Ca²⁺) — 10 mEq to mg

  • Given: 10 mEq of Calcium (Ca²⁺)
  • Molecular weight of Ca: 40.08 g/mol
  • Valency of Ca²⁺: 2
  • Formula: mg = (mEq × MW) ÷ valency
  • Calculation: (10 × 40.08) ÷ 2 = 200.4 mg

Example 3: Sodium (Na⁺) — 500 mg to mEq

  • Given: 500 mg of Sodium (Na⁺)
  • Molecular weight of Na: 23 g/mol
  • Valency of Na⁺: 1
  • Formula: mEq = (mg × valency) ÷ MW
  • Calculation: (500 × 1) ÷ 23 = 21.74 mEq

Common mEq to mg Conversions — Reference Table

The table below shows common milliequivalent to milligram conversions for the most frequently used medical ions. Use the mEq to mg converter above to calculate any specific value instantly.

IonMW (g/mol)Valency1 mEq =10 mEq =20 mEq =
Sodium (Na⁺)23123 mg230 mg460 mg
Potassium (K⁺)39.1139.1 mg391 mg782 mg
Calcium (Ca²⁺)40.08220.04 mg200.4 mg400.8 mg
Magnesium (Mg²⁺)24.31212.16 mg121.6 mg243.1 mg
Chloride (Cl⁻)35.45135.45 mg354.5 mg709 mg
Bicarbonate (HCO₃⁻)61.02161.02 mg610.2 mg1220.4 mg
Phosphate (PO₄³⁻)94.97331.66 mg316.6 mg633.1 mg

Medical Uses of mEq — Why This Unit Matters

Milliequivalents are the standard unit for expressing electrolyte concentrations in blood, urine, and IV fluids. The mEq to mg calculator is used daily in hospitals, pharmacies, and clinical laboratories for the following reasons.

Electrolyte panels and blood tests

Blood electrolyte reports express sodium, potassium, chloride, and bicarbonate in mEq/L (milliequivalents per litre). Normal reference ranges for these values are defined in mEq/L — for example, serum sodium is normally 136–145 mEq/L and potassium is 3.5–5.0 mEq/L. Understanding and converting these values requires a reliable milliequivalent calculator.

IV fluid and electrolyte replacement

When prescribing IV potassium or sodium replacement, doses are ordered in mEq — for example, 40 mEq KCl in 1 litre of normal saline. The mg to mEq calculator helps pharmacists and nurses verify doses when preparing infusions from products labelled in mg.

Oral electrolyte supplements

Many oral potassium and magnesium supplements list their doses in both mg and mEq on the label. A 10 mEq potassium chloride tablet contains 391 mg of potassium — knowing this conversion helps patients and clinicians compare products accurately.

Pharmacology and drug dosing

  • Potassium chloride (KCl) — IV and oral doses are prescribed in mEq. The mEq to mg conversion is essential for calculating equivalent doses from different formulations.
  • Calcium gluconate — doses are given in mEq of calcium, requiring the divalent conversion formula (valency 2).
  • Magnesium sulfate — used in eclampsia and cardiac arrhythmias, doses are expressed in mEq or grams, requiring careful conversion.
  • Sodium bicarbonate — used in metabolic acidosis, doses are prescribed in mEq and must be converted to mg or mL for administration.

Sources & References

→ IUPAC Technical Report 2021 — DOI: 10.1515/pac-2019-0603 — Atomic weights of the elements

→ NIST Chemistry WebBook (SRD 69) — National Institute of Standards and Technology

→ National Institutes of Health (NIH) — Electrolyte reference ranges and clinical guidelines

→ igcsepro.org, caesarcipher.org — Milliequivalent calculator methodology reference

Frequently Asked Questions — mEq to mg Converter

What is mEq in medical terms? +
mEq stands for milliequivalent — a unit used in medicine to express the chemical activity of an ion in solution. Unlike milligrams which only measure mass, milliequivalents account for both the mass and the electrical charge (valency) of an ion. This makes mEq the standard unit for reporting electrolyte concentrations in blood tests, IV fluids, and clinical prescriptions. One mEq is one thousandth of one equivalent.
How do I convert mEq to mg? +
To convert mEq to mg, use this formula: mg = (mEq × molecular weight) ÷ valency. For example, to convert 20 mEq of potassium (MW 39.1, valency 1): mg = (20 × 39.1) ÷ 1 = 782 mg. For calcium (MW 40.08, valency 2): 10 mEq = (10 × 40.08) ÷ 2 = 200.4 mg. The mEq to mg converter above performs this calculation automatically for any ion you select.
Why is valency important in the mEq to mg calculation? +
Valency represents the electrical charge of an ion — how many electrons it can donate or accept. Monovalent ions like sodium (Na⁺) and potassium (K⁺) have a valency of 1. Divalent ions like calcium (Ca²⁺) and magnesium (Mg²⁺) have a valency of 2. Because milliequivalents are defined by chemical activity rather than mass alone, valency must be included in the milliequivalent calculator formula. Ignoring valency would produce incorrect results for divalent ions.
What is the formula for mEq calculation? +
There are two formulas depending on the direction of conversion. To convert mEq to mg: mg = (mEq × molecular weight) ÷ valency. To convert mg to mEq: mEq = (mg × valency) ÷ molecular weight. Both formulas require the molecular weight of the ion in g/mol and its valency. The mEq to mg converter on this page applies these formulas automatically when you select an ion from the dropdown.
What is mEq used for in hospitals? +
In hospitals, mEq is used to express electrolyte concentrations in blood tests (e.g., serum sodium 140 mEq/L, potassium 4.0 mEq/L), prescribe IV electrolyte replacements (e.g., 40 mEq KCl in 1 litre saline), and dose medications such as sodium bicarbonate, calcium gluconate, and magnesium sulfate. Using mEq rather than mg ensures that the chemical activity of the ion is accurately represented, which is critical for safe clinical dosing.
How many mg is 1 mEq of potassium? +
1 mEq of potassium (K⁺) equals 39.1 mg. This is because potassium has a molecular weight of 39.1 g/mol and a valency of 1. Using the formula: mg = (1 × 39.1) ÷ 1 = 39.1 mg. A common 10 mEq potassium chloride tablet therefore contains 391 mg of potassium. Use the mEq to mg calculator above to convert any potassium dose instantly.
How many mg is 1 mEq of sodium? +
1 mEq of sodium (Na⁺) equals 23 mg. Sodium has a molecular weight of 23 g/mol and a valency of 1. Using the formula: mg = (1 × 23) ÷ 1 = 23 mg. Normal serum sodium is 136–145 mEq/L, which corresponds to approximately 3,128–3,335 mg per litre of blood. The mEq to mg converter on this page calculates sodium conversions for any mEq value you enter.
Can this mEq to mg calculator be used for any ion? +
Yes — this milliequivalent calculator includes 7 preset ions (sodium, potassium, calcium, magnesium, chloride, bicarbonate, and phosphate) with pre-filled molecular weights and valencies. For any other ion not in the list, select Custom and enter the molecular weight and valency manually. The calculator will then apply the standard mEq to mg formula to produce an accurate result for any substance.

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