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Health

Electrolyte Calculator

Sodium, potassium and magnesium replacement for long or hot sessions.

Enter your values

ⓘ Live results

Results
Sodium to replace
2,700 mg
Sodium per hour
1,080 mg/h
Covered by your drink
1,500 mg (56%)
Extra sodium needed
1,200 mg (about 3 salt caps)
Fluid to replace
3 litres
Potassium target
600 mg
Magnesium target
90 mg

Working

  1. 11.2 L/h x 2.5 h = 3 L sweat
  2. 23 L x 900 mg/L = 2,700 mg sodium

Quick answer

Sweat carries roughly 400 to 1500 mg of sodium per litre. Replacement should match your sweat rate, session length and how salty you sweat.

sodium mg = litres sweat x sodium concentration

How to use the Electrolyte Calculator

  1. 1Estimate sweat rate by weighing yourself before and after an hour of training, adding any fluid drunk.
  2. 2Judge saltiness from white marks on your kit and stinging eyes.
  3. 3Compare the total against what your drink mix already supplies and top up the gap.

Worked example

Using the values the calculator loads with:

Inputs

  • Sweat rate1.2 litres/hour
  • Session length2.5 hours
  • Sweat saltinessAverage
  • Sodium in your drink mix500 mg per litre

Results

  • Sodium to replace2,700 mg
  • Sodium per hour1,080 mg/h
  • Covered by your drink1,500 mg (56%)
  • Extra sodium needed1,200 mg (about 3 salt caps)
  • Fluid to replace3 litres
  • Potassium target600 mg
  • Magnesium target90 mg
  1. 1.2 L/h x 2.5 h = 3 L sweat
  2. 3 L x 900 mg/L = 2,700 mg sodium

Frequently asked questions

Do I need electrolytes for a one hour session?

Usually not, unless it is very hot. Below about 90 minutes plain water and a normal diet cover the losses for most people.

Can I take too much sodium?

Yes. Overshooting causes stomach upset and thirst. Match replacement to real losses instead of drinking the strongest mix available.

About this calculator

Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.