HydrationGuideHow much sodium do you lose in sweat? For most people, between 400 and 1,600 mg per litre — a spread wide enough that the same session can be a non-event for one athlete and a genuine deficit for another. The number above multiplies your sweat volume by the published concentration range for your saltiness, instead of pretending everyone sweats the same brine.
Sweat sodium concentration chart
Laboratory values in athletes run from roughly 18 to 71 mmol/L (about 400 to 1,600 mg/L), with the whole-body mean near 36 mmol/L (~830 mg/L). The bands below are that measured spread, split the way the calculator uses it — most people sit in the middle and cannot tell without a sweat test.
| Sweater type | Sodium (mg/L) | Sodium (mmol/L) | Visible signs |
|---|---|---|---|
| Barely salty | 400–700 | 17–30 | No visible residue, sweat rarely stings the eyes |
| Average | 600–1,100 | 26–48 | Occasional faint white marks on dark kit after hard sessions |
| Very salty | 1,000–1,600 | 43–70 | White crust on skin, cap, or kit; sweat stings the eyes |
Concentration bands from Baker (2017); mmol/L converted at 23 mg sodium per mmol. Genetics, diet, and heat acclimation all move the number, and acclimated athletes typically conserve more sodium at the same sweat rate.
Worked examples: real sessions, real losses
Five sessions run through the exact model behind the calculator above. Note how duration and saltiness matter more than intensity: the four-hour hike out-loses the hard 90-minute match for an average sweater.
| Session | Sweat | Sodium lost | ≈ Table salt |
|---|---|---|---|
| Half-hour easy run, mild day | 0.4 L | 250–450 mg | 0.8 g |
| One-hour warm session | 1.2 L | 700–1,300 mg | 2.5 g |
| 90-minute match, salty sweater | 2.1 L | 2,100–3,350 mg | 6.9 g |
| Two-hour ride, barely salty | 2.0 L | 800–1,400 mg | 2.5 g |
| Four-hour hike, steady pace | 2.4 L | 1,450–2,650 mg | 5.1 g |
How the calculator works
The model is two multiplications kept honest. Sweat volume is your sweat rate times your session length. Sodium lost is that volume times a concentration band from the Baker (2017) review of sweat testing in athletes — the same table the sweat rate calculator uses, so the two tools always agree.
What the model deliberately does not do: predict your personal concentration. Sweat sodium is not related to body weight or fitness in any way a calculator could use, and the honest options are a wide range or false precision. The saltiness setting narrows the band using visible signs, which is the best signal available without a laboratory sweat test.
Results are rounded to 50 mg steps and shown as ranges throughout. A figure like "1,037 mg" would imply the model knows more than it does.
Replacing it: food first, drinks when it counts
For sessions under an hour, the answer is your next meal. A slice of bread carries ~150 mg of sodium, a bowl of soup 700–900 mg, a pickle around 800 mg — normal eating replaces normal sweating without any product involved.
During long or hot sessions, replacement moves into the bottle. The ACSM's 0.5–0.7 g/L guidance brackets what commercial sports drinks (~460 mg/L) and zero-sugar packets (~1,000 mg/L) provide. The homemade electrolyte calculator matches either ratio from kitchen salt for a few cents per litre, scaled to your bottle.
The one direction to avoid: replacing hours of salty sweat with plain water alone. That dilutes blood sodium — exercise-associated hyponatremia — which is more dangerous than mild dehydration because it looks similar and is treated oppositely.
Frequently asked questions
How much sodium do you lose in sweat?
Roughly 400 to 1,600 mg per litre of sweat, with the average around 830 mg per litre. Total loss is that concentration times how much you sweat: an hour at a typical 1.2 litres per hour costs an average sweater about 1,000 mg of sodium, and a salty sweater in the same session can lose over 1,500 mg. The several-fold spread between people is why this calculator gives ranges rather than one number.
How do I know if I am a salty sweater?
White crust or gritty residue on your skin, cap, or dark clothing after sessions, and sweat that stings your eyes, are the visible signs. They are a rough signal rather than a test: only a laboratory sweat test measures your actual concentration. If you regularly see salt crust, assume the high end of the range and replace accordingly on long sessions.
Do I need to replace sodium during exercise?
Under about an hour in mild conditions, no: normal food afterwards covers it. Past an hour of real sweating, and especially in heat, replacement during exercise starts to matter, because replacing litres of salty sweat with plain water alone dilutes blood sodium. The ACSM recommends 0.5 to 0.7 grams of sodium per litre of fluid for exercise over an hour.
What happens if I only drink water after heavy sweating?
The water replaces volume but not the sodium that left with it, so blood sodium becomes more dilute. Taken far enough over a long day, that is exercise-associated hyponatremia: headache, nausea, confusion, and in severe cases seizures. It is more dangerous than mild dehydration because the early symptoms look similar and the treatment is the opposite. Salty food or an electrolyte drink alongside the water prevents it.
How should I replace the sodium I lose?
For most sessions, ordinary salty food with your post-exercise meal does the job for free. For long or hot sessions where you are replacing as you go, a drink in the 500 to 1,000 mg per litre range works: commercial sports drinks sit near 460 mg per litre, zero-sugar electrolyte packets near 1,000 mg per litre, and a homemade mix from table salt costs a few cents to match either.
Does sweating out sodium lower my blood pressure?
Sweating is not a treatment for sodium intake. Losses during exercise are real but the body regulates blood sodium tightly, and any deficit is corrected at the next salty meal. If you have high blood pressure, the number that matters is what you eat day to day, and how much sodium is right for you is a question for your doctor, particularly on diuretics or other blood pressure medicines.
How accurate is a sweat sodium estimate?
The volume part is as good as your sweat rate number, which one weigh-in test makes quite accurate. The concentration part is honest but wide: without a laboratory sweat test, your true value could sit anywhere in your band, which spans roughly two-fold. Treat the result as planning guidance for what to eat and drink, not as a physiological measurement.
Sources
- Baker, L.B. (2017). Sweating Rate and Sweat Sodium Concentration in Athletes: A Review of Methodology and Intra/Interindividual Variability. Sports Medicine 47(S1).
- Baker, L.B. et al. (2016). Normative data for regional sweat sodium concentration and whole-body sweating rate in athletes. Journal of Sports Sciences.
- American College of Sports Medicine (2007). Position Stand: Exercise and Fluid Replacement.
- FDA. Sodium in Your Diet: the 2,300 mg daily value.