Electrolyte Balance Calculator

Electrolytes are minerals in your blood and bodily fluids that carry an electric charge. They are essential for muscle contractions, nerve signals, hydration, and pH balance. When you sweat, you lose electrolytes, not just water, and the one you lose in quantity is sodium.

The Four Key Electrolytes

Sodium (Na⁺)

The primary electrolyte in blood plasma. Regulates fluid balance and blood pressure. Reference range: 135–145 mEq/L in blood. The US Adequate Intake for adults is 1,500 mg, and 2,300 mg is the ceiling public health advice sets. Athletes and heavy sweaters may need 3,000–5,000 mg on training days.

Potassium (K⁺)

The primary electrolyte inside cells. Critical for heart rhythm, muscle function, and blood pressure regulation. The US Adequate Intake is 2,600 mg for women and 3,400 mg for men. Found in bananas, sweet potatoes, avocados, and spinach.
Sweat carries about a fifth as much potassium as sodium by weight, so training barely changes this figure. If a sports drink is being sold to you on its potassium content, that is marketing rather than physiology.

Magnesium (Mg²⁺)

Involved in over 300 enzymatic reactions. Essential for muscle relaxation, sleep, energy production, and bone health. The Recommended Dietary Allowance is 310 mg for women aged 19 to 30 and 320 mg from 31, and 400 mg and 420 mg for men. It goes by sex and age, not by body weight. Surveys find many adults fall short of it.

Calcium (Ca²⁺)

Essential for bone density, muscle contraction, and nerve transmission. The allowance is 1,000 mg a day for most adults, rising to 1,200 mg for women over 50 and men over 70. Found in dairy, leafy greens, and fortified foods.

Sweat and Electrolyte Loss

A typical person loses approximately 0.5–1.5 liters of sweat per hour of moderate exercise. Sweat holds roughly 200 to 2,000 mg of sodium per litre, about 1,000 mg on average, and the spread between people is wide enough that a “salty sweater” can lose four times what a neighbour does. White crust on a cap or a shirt after a long session is the usual sign.

How the calculator gets its numbers

Potassium, magnesium and calcium start from the US intake figures for your sex and age, and training adds a little to the first two.
Sodium starts at the 1,500 mg Adequate Intake and adds an allowance for sweat. That allowance grows with the activity and sweat choices and scales with body weight against a 70 kg reference, because a bigger body makes more heat and sweats more doing the same work. It stops at 5,000 mg.

A 70 kg athlete training hard in the heat comes out at 4,800 mg of sodium, and the same training at 50 kg gives about 3,860 mg.

These are general guidelines for healthy adults. Kidney disease, heart failure and several blood pressure drugs change them a great deal, often in the opposite direction, so check with a doctor before acting on them.

Metric and Imperial Support

Enter weight in kilograms (kg) or pounds (lbs). 1 kg = 2.205 lbs.