Electrolyte Replacement Calculator

About this calculator

This calculator estimates sodium and potassium losses through sweat during exercise, based on typical sweat electrolyte concentrations (sodium averages roughly 800-1000 mg per liter of sweat, though it varies significantly between individuals, with 'salty sweaters' losing considerably more) multiplied by an estimated total sweat volume for the session, giving a total electrolyte loss figure in milligrams.

Endurance athletes — marathoners, cyclists, and anyone training in heat for extended periods — track sweat sodium loss because inadequate replacement during long sessions is a contributing factor in exercise-associated hyponatremia (dangerously low blood sodium from excessive plain-water intake without electrolyte replacement) and in cramping and fatigue during a workout. Sports scientists use sweat-testing protocols (weighing an athlete before and after exercise, accounting for fluid intake) to individualize these estimates, since sweat rate and sodium concentration vary widely between athletes.

This calculator takes your exercise duration, sweat rate, and sweat sodium concentration, then returns your estimated sodium and potassium losses, so you can plan electrolyte replacement that matches what you're actually losing.