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Electrolyte Replacement Calculator

Work out electrolyte replacement instantly with clear inputs, formula shown and shareable results.

About Electrolyte Replacement Calculator

Multiplies sweat rate, duration and sweat sodium concentration to give the sodium lost during exercise and the concentration needed to replace it.

Formula

Sweat sodium loss

Sodium lost (mg) = sweat rate (L/h) x hours x sweat sodium concentration (mg/L); salt (g) = sodium (mg) x 2.542 / 1000

Worked example

With the default values below, Electrolyte Replacement Calculator returns Sodium lost in sweat of 2,160. Change any input above and every figure here is recalculated in your browser.

Inputs used

Sweat rateaccepts 0.2–3.5 L/h
1.2 L/h
Durationaccepts 0.25–12 h
2 h
Sweat sodium concentrationaccepts 200–2,000 mg/L
900 mg/L

Results

Sodium lost in sweat
2,160 mg
Fluid lost
2.400 L
Sodium loss expressed as salt
5.491 g
Sodium concentration needed to replace fully
900 mg/L

Step by step

  1. 1Values used
  2. 2Sweat sodium loss
  3. 3Sodium lost in sweat= 2,160 mg
  4. 4Fluid lost= 2.400 L
  5. 5Sodium loss expressed as salt= 5.491 g
  6. 6Sodium concentration needed to replace fully= 900 mg/L

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.
  • This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

Frequently Asked Questions

How variable is sweat sodium?

Very. It ranges from about 200 to 2,000 mg per litre between individuals and falls somewhat with heat acclimatisation.

When does sodium replacement matter?

In sessions over about two hours, in heat, and in salty sweaters where hyponatraemia risk rises with plain water intake.

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