Electrolyte Calculator
Sodium, potassium and magnesium replacement for long or hot sessions.
Enter your values
Enter the sweat rate in litres/hour.
Enter the session length in hours.
Choose one of: Low (no salt marks), Average, Salty (white marks on kit).
Enter the sodium in your drink mix in mg per litre.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- 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
- 11.2 L/h x 2.5 h = 3 L sweat
- 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
At a glance
| What it does | Sodium, potassium and magnesium replacement for long or hot sessions. |
|---|---|
| Category | Health |
| Inputs needed | Sweat rate, Session length, Sweat saltiness, Sodium in your drink mix |
| Main output | Sodium to replace |
| Formula | sodium mg = litres sweat x sodium concentration |
| Cost | Free — no sign-up, no download |
How to use the Electrolyte Calculator
- 1Estimate sweat rate by weighing yourself before and after an hour of training, adding any fluid drunk.
- 2Judge saltiness from white marks on your kit and stinging eyes.
- 3Compare the total against what your drink mix already supplies and top up the gap.
Inputs explained
- Sweat rate(litres/hour)
- Enter the sweat rate in litres/hour.
- Session length(hours)
- Enter the session length in hours.
- Sweat saltiness
- Choose one of: Low (no salt marks), Average, Salty (white marks on kit).
- Sodium in your drink mix(mg per litre)
- Enter the sodium in your drink mix in mg per litre.
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
- 1.2 L/h x 2.5 h = 3 L sweat
- 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.
What do I need to enter into the Electrolyte Calculator?
Just 4 values: sweat rate, session length, sweat saltiness, sodium in your drink mix. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Electrolyte Calculator work out the 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. It applies the formula sodium mg = litres sweat x sodium concentration and shows the working so you can check each step by hand.
Is the Electrolyte Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.