mEq to mg Converter

What is a milliequivalent (mEq)?

A milliequivalent (mEq) measures the amount of a charged particle (an ion) in terms of its chemical combining power – essentially, how much electrical charge it carries – rather than its weight. It is used for electrolytes such as sodium, potassium, chloride, bicarbonate, calcium and magnesium, in blood tests, intravenous fluids, and medicine and supplement labels.

The link between mEq, millimoles (mmol) and milligrams (mg) is:

• mEq = mmol × valence (the size of the ion's charge)
• mg = mmol × molar mass (g/mol)

Putting those together:

mg = mEq × molar mass ÷ valence

mEq = mg × valence ÷ molar mass

For ions with a single charge – sodium (Na⁺), potassium (K⁺), chloride (Cl⁻), bicarbonate (HCO₃⁻) – 1 mEq = 1 mmol. For ions with a double charge – calcium (Ca²⁺), magnesium (Mg²⁺) – 1 mEq = 0.5 mmol.

The converter above has three modes: mEq → mg, mg → mEq (with grams as an option) and a custom mode where you enter any molar mass and valence. It includes the common ions and the common salts used in medicines.

mEq to mg conversion table

Molar masses are from standard atomic weights; small differences in published tables come from rounding.

Worked examples

• 20 mEq of potassium chloride in mg: 20 × 74.55 ÷ 1 = 1,491 mg (about 1.5 g) of KCl. That contains 20 × 39.10 = 782 mg of elemental potassium.
• 2,300 mg of sodium in mEq: 2,300 × 1 ÷ 22.99 = 100 mEq – the US Dietary Guidelines' upper daily limit for sodium for adults.
• 1 g of table salt (NaCl): 1,000 ÷ 58.44 = 17.1 mEq of sodium (and 17.1 mEq of chloride), equal to about 393 mg of sodium.
• 1 mEq of calcium in mg: 40.08 ÷ 2 = 20.04 mg of elemental calcium.
• 1 g of calcium gluconate: 1,000 × 2 ÷ 430.37 = 4.65 mEq of calcium, or about 93 mg of elemental calcium.
• 400 mg of magnesium (elemental): 400 × 2 ÷ 24.31 = 32.9 mEq (16.5 mmol).

Salt vs element: the most common confusion

Medicine and supplement labels may state the amount of the whole salt (for example "potassium chloride 750 mg") or the amount of the element (for example "potassium 99 mg" or "10 mEq"). These are very different numbers:

When converting, choose the salt in the converter if your label gives the weight of the salt, and the ion if it gives the weight of the element. Getting this wrong can mean a large error.

mEq/L in blood tests

Electrolytes on a basic metabolic panel (BMP) are reported per litre:

Ranges for sodium, potassium, chloride, bicarbonate, calcium (mg/dL) and magnesium (mg/dL) are from the NBME reference values. Calcium and magnesium are usually reported in mg/dL in the US and mmol/L elsewhere; mEq/L is less common for them. See the calcium converter and magnesium converter.

Why mEq is useful

Body fluids must be electrically neutral: the total positive charge equals the total negative charge. Expressing ions in mEq makes it easy to check that balance. It is the basis of the anion gap: sodium − (chloride + bicarbonate), all in mEq/L, which reveals "unmeasured" negative ions such as ketones or lactate. Try the anion gap calculator.

Valence explained

Valence is the size of an ion's electrical charge, ignoring whether it is positive or negative:

For a salt, the valence used is the charge of the ion you are interested in. For potassium chloride (KCl), each molecule releases one K⁺ and one Cl⁻, so 1 mmol KCl = 1 mEq K⁺ = 1 mEq Cl⁻. For calcium chloride (CaCl₂), each molecule releases one Ca²⁺ and two Cl⁻, so 1 mmol CaCl₂ = 2 mEq of calcium and 2 mEq of chloride.

Phosphate is a special case: at body pH it exists as a mixture of HPO₄²⁻ and H₂PO₄⁻, so its average valence is about 1.8 and depends on pH. For this reason, phosphate is usually prescribed and reported in mmol rather than mEq, and the converter does not include it as a preset. If you need it, use custom mode and state the valence you assumed.

Step by step: converting any substance

1. Identify exactly what the amount refers to – the salt (for example potassium chloride) or the element (potassium). Labels usually say which.
2. Find the molar mass of that form, in g/mol (mg/mmol). For hydrated salts, include the water of crystallisation.
3. Find the valence of the ion of interest.
4. Apply the formula: mg = mEq × molar mass ÷ valence, or mEq = mg × valence ÷ molar mass.
5. Check the result with a known anchor – for example, 1 g of NaCl ≈ 17 mEq, 1 mEq of potassium ≈ 39 mg.

Example with a hydrated salt: how many mEq of magnesium are in 2 g of magnesium sulfate heptahydrate (MgSO₄·7H₂O, 246.47 g/mol)? 2,000 × 2 ÷ 246.47 = 16.2 mEq (8.1 mmol), containing about 197 mg of elemental magnesium. Using the anhydrous molar mass (120.37 g/mol) by mistake would give 33.2 mEq – twice the true value.

mmol, mEq and mOsm

Three related units appear on lab reports and fluid labels:

Osmolality, measured in mOsm/kg, describes how concentrated body fluids are. You can estimate serum osmolality from sodium, glucose and BUN with the serum osmolality calculator.

Common mistakes

• Mixing up salt and element. 1,500 mg of potassium chloride is not 1,500 mg of potassium – it contains about 787 mg.
• Forgetting valence for calcium and magnesium. 10 mmol of calcium is 20 mEq, not 10.
• Using anhydrous instead of hydrated molar masses, or vice versa, for salts such as calcium chloride and magnesium sulfate.
• Confusing mEq with mEq/L. mEq is an amount; mEq/L is a concentration. A serum potassium of 4 mEq/L says nothing about how many mEq are in a tablet.
• Mixing g and mg. The converter lets you choose the mass unit explicitly to avoid a 1,000-fold error.
• Rounding too early. Keep at least three significant figures until the final step.

A short history of the equivalent

The concept of chemical "equivalents" dates back to the late 18th and early 19th centuries, when chemists noticed that substances react in fixed proportions by weight. In clinical medicine, the milliequivalent became standard for electrolytes in the mid-20th century because it made the balance of positive and negative ions easy to see. The International System of Units (SI) does not include the equivalent; the SI unit of amount of substance is the mole, which is why many countries report electrolytes in mmol/L. For sodium, potassium, chloride and bicarbonate, the numbers are identical either way.

Converting concentrations: mEq/L to mg/dL

The same formula works for concentrations, with an extra factor of 10 because a decilitre is one-tenth of a litre:

mg/dL = mEq/L × molar mass ÷ (valence × 10)

mEq/L = mg/dL × valence × 10 ÷ molar mass

Sodium and potassium are almost never reported in mg/dL in clinical practice, but the conversion can be useful in nutrition science or when reading older literature.

Quick-reference anchors

Memorising a few anchors makes it easy to sanity-check any conversion:

• 1 mEq of sodium ≈ 23 mg; 100 mEq ≈ 2.3 g of sodium.
• 1 mEq of potassium ≈ 39 mg; 1 g of potassium ≈ 25.6 mEq.
• 1 g of salt ≈ 17 mEq of sodium ≈ 393 mg of sodium.
• 1 g of potassium chloride ≈ 13.4 mEq of potassium.
• 1 mEq of calcium ≈ 20 mg; 1 mmol of calcium = 2 mEq ≈ 40 mg.
• 1 mEq of magnesium ≈ 12 mg; 1 mmol of magnesium = 2 mEq ≈ 24 mg.

If a converted value is wildly different from these anchors, check whether you selected the salt rather than the ion, or g rather than mg.

Sodium in food: mg and mEq

Nutrition labels list sodium in mg, while medical diets for heart failure or kidney disease are sometimes described in mEq or grams of sodium:

To convert sodium to salt, multiply by 2.54 (58.44 ÷ 22.99). The Dietary Guidelines for Americans recommend that adults limit sodium to less than 2,300 mg per day; WHO recommends less than 2,000 mg of sodium (5 g of salt) per day for adults.

Potassium in food and supplements

Potassium in foods is listed in mg on US nutrition labels. 1,000 mg of potassium is about 25.6 mEq. Many over-the-counter potassium supplements in the US contain no more than 99 mg of potassium per serving. People with kidney disease or taking certain blood-pressure medicines need to be cautious with potassium; discuss supplements with your clinician first.

Medicine and IV fluid labels

Intravenous fluids are labelled in mEq/L. For example, 0.9% sodium chloride ("normal saline") contains 9 g of NaCl per litre: 9,000 ÷ 58.44 = 154 mEq/L of sodium and 154 mEq/L of chloride. Lactated Ringer's solution contains about 130 mEq/L of sodium, 4 mEq/L of potassium and 109 mEq/L of chloride, among other components.

This page is a unit converter only. It does not recommend amounts of any electrolyte; doses of potassium, sodium, calcium, magnesium and bicarbonate must come from a prescriber or the product label. If you are unsure, ask a pharmacist.