Electrolyte needs estimator
Sweat is mostly water with some salt. For most sessions, your next meal puts it back. For long, hot events it is worth knowing roughly how much you lose.
Your details
Salt lost in 1.5 litres of sweat
3.0 g
salt (1.2 g sodium), typical sweat
- Salty sweater?white marks on kit, stinging eyes
- Everyday upper limit for salt6 g
- Typical sports drinkabout 0.5 to 1.2 g salt a litre
- Your drinkadd how much you will drink and the salt per litre on its label
For most sessions under two hours, your next meal replaces this. Long, hot events are when electrolyte drinks earn their keep. Drinking lots of plain water in a long event without salt can be risky.
Confusion, headache, being sick or swelling after a long event can mean low sodium (hyponatraemia). Get medical help straight away.
The working
Litres times sodium per litre
Sweat sodium varies a lot, roughly 0.2 to 2 g per litre. We use 0.4 g for low, 0.8 g for typical and 1.4 g for salty sweaters, then convert sodium to salt by multiplying by 2.5. 1.5 litres of typical sweat is 1.2 g of sodium, or 3.0 g of salt.
Your drink
How much it puts back
UK labels give salt per 100 ml or per litre. Add how much you will drink and its salt per litre: 1 litre at 1 g a litre puts back 1.0 g of the 3.0 g above, a third, leaving 2.0 g for your next meal. Over a 3 hour event that loss is 1.0 g of salt (400 mg sodium) an hour. For sessions over 2 hours, the ACSM suggests drinks with 20 to 30 mmol of sodium a litre, about 1.2 to 1.7 g of salt.
When it matters
Most sessions need nothing extra
For workouts under about two hours, normal meals replace sodium easily, and most UK diets already have more than enough salt. Electrolyte drinks help in long events (marathons, long rides, hot weather), especially for salty sweaters, and help you hold on to the fluid you drink.
A safety note
Water alone in long events
Drinking large amounts of plain water over several hours, without any salt, can lower blood sodium. Symptoms include headache, confusion, nausea and swelling. It is rare, but it is why long event drinks usually contain sodium.
Read with care
What this cannot tell you
- Exact sweat sodiumOnly a sweat test measures yours.
- Medical conditionsBlood pressure and kidney conditions may need different advice.
- Potassium and othersSweat also has small amounts of potassium and magnesium.
Questions
Common questions
Do I need electrolyte drinks?
Not usually for gym sessions or runs under two hours. They help in long or hot events.
How much salt do you lose in sweat?
Typically 1 to 3 g of salt per litre of sweat, though some people lose more.
What is a salty sweater?
Someone with high sweat sodium; white marks on clothes and stinging eyes are clues.
Sources
- Sawka MN et al. Exercise and fluid replacement (ACSM position stand). Med Sci Sports Exerc 2007
- Thomas DT et al. Nutrition and athletic performance (ACSM joint position). Med Sci Sports Exerc 2016
- NHS: salt, the facts
Last checked 21 October 2026. Spotted something wrong? Tell us and we will fix it.
After a long event
Confusion, a bad headache, being sick or swelling after a long event can mean low blood sodium. Get medical help straight away, or call 999.
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