How much sodium per hour?
Most sports nutrition guidance for events longer than about two hours lands on roughly 300–600 mg of sodium per hour, rising towards 800–1,000 mg or more for heavy, salty sweaters in hot weather. For runs shorter than about 75 minutes, water (or nothing) is enough: you have plenty of sodium in reserve.
The right number depends on two things: how much you sweat and how salty your sweat is. Both vary several-fold between runners, which is why a single number does not fit everyone.
Sodium lost per hour
Sodium lost per hour = sweat rate × sweat sodium concentration. This table shows typical combinations:
| Sweat rate | Not very salty (500 mg/L) | Average (950 mg/L) | Salty (1,500 mg/L) |
|---|---|---|---|
| 0.5 L/h (17 fl oz) | 250 mg/h | 475 mg/h | 750 mg/h |
| 0.75 L/h (25 fl oz) | 375 mg/h | 712 mg/h | 1,125 mg/h |
| 1.0 L/h (34 fl oz) | 500 mg/h | 950 mg/h | 1,500 mg/h |
| 1.25 L/h (42 fl oz) | 625 mg/h | 1,188 mg/h | 1,875 mg/h |
| 1.5 L/h (51 fl oz) | 750 mg/h | 1,425 mg/h | 2,250 mg/h |
| 2.0 L/h (68 fl oz) | 1,000 mg/h | 1,900 mg/h | 3,000 mg/h |
Sweat sodium is often quoted in mmol/L: multiply by 23 to get mg/L (40 mmol/L ≈ 920 mg/L).
How the calculator estimates your sweat rate
If you have not measured it, the calculator estimates sweat rate from the heat your body has to get rid of. Running burns roughly 1 kcal per kg of body weight per km, about 80 % of which becomes heat. The warmer it is, the more of that heat has to leave through evaporating sweat (each litre removes about 580 kcal), and humid air means more sweat drips off without cooling you. The result is typically 0.4–0.7 L/h on cool days and 1–1.5 L/h or more in the heat. Weighing yourself before and after a run is far more accurate: use the sweat rate calculator.
Why replace only part of what you lose
You do not need to replace every milligram during a race. Your body carries a large sodium reserve and copes with a moderate deficit; what matters most is not diluting your blood sodium by drinking far more water than you sweat. The calculator aims to replace about half of your estimated loss, kept between 300 and 1,000 mg an hour, and suggests drinking somewhat less than you sweat.
Do not overdrink. Exercise-associated hyponatremia (low blood sodium) mostly happens to runners who drink more than they sweat during long, slow events and gain weight during the race. Taking salt does not make overdrinking safe. Drink to thirst, and never so much that you finish heavier than you started.
Where the sodium comes from
| Source | Typical sodium |
|---|---|
| Energy gel | About 20–200 mg; many around 50–100 mg (check the label) |
| Sports drink | About 200–500 mg per 500 ml; high-sodium mixes 750–1,000 mg |
| Salt capsule or tablet | About 100–250 mg each |
| Table salt | About 575 mg in ¼ teaspoon (salt is about 40 % sodium) |
| Salted pretzels, crisps, broth (ultra aid stations) | Varies: often 200–800 mg per serving |
Practical tips
- Practise in training. Try your race-day sodium and fluid plan on long runs; stomachs need training too.
- Carbs too. Sodium is only part of race nutrition: plan your gels and carbs per hour with the race fueling calculator.
- Spread it out. Small doses every 20–30 minutes sit better than one big dose an hour.
- Hot races: sweat rate can double; also slow your pace with the heat pace calculator.
- Pre-loading: a salty meal the evening before and a drink with sodium in the last hour before a hot race can help heavy sweaters start well hydrated.
- American College of Sports Medicine (2007). Exercise and fluid replacement: position stand. Medicine & Science in Sports & Exercise 39(2): 377–390.
- Baker LB (2017). Sweating rate and sweat sodium concentration in athletes: a review of methodology and intra/interindividual variability. Sports Medicine 47(Suppl 1): 111–128.
- Hew-Butler T. et al. (2015). Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference. Clinical Journal of Sport Medicine 25(4): 303–320.
- Sweat-rate estimates are approximations for planning; measure your own sweat rate for best results. Not medical advice. Last reviewed October 2026.
Last reviewed: September 2026 · Health disclaimer