Electrolyte Replacement Calculator

This calculator estimates total sweat volume before translating that volume into fluid and mineral quantities. Sweat rate and exercise duration are multiplied together, then climate applies a factor of 0.85 for cool conditions, 1.0 for moderate conditions, or 1.2 for hot conditions. That adjusted volume is the shared foundation for every displayed result, so a longer session or higher sweat rate raises all four outputs at the current settings. Sodium is individualized one step further by multiplying adjusted liters of sweat by the entered sodium concentration in milligrams per liter. Potassium and magnesium do not use that concentration field; they apply fixed assumptions of 200 milligrams and 12 milligrams per liter respectively.

The fluid target is 150 percent of estimated sweat volume and is rounded to hundredths of a liter. Thus, sweat sodium concentration can materially alter sodium while leaving potassium, magnesium, and total fluid unchanged. Climate in this model scales sweat volume, despite the nearby comment describing concentration, so hot conditions increase all estimated losses by 20 percent relative to moderate and cool conditions reduce them by 15 percent. The tool does not subtract drinks consumed during exercise, distinguish replacement during versus after activity, or account for urine, altitude, acclimatization, kidney or heart conditions, and product composition. A measured sweat rate and sodium test are more specific than the defaults.