Hydration Calculator: Water Needs for Training

How much water do you need each day, and how much should you drink before, during and after training? This hydration calculator gives you a daily fluid baseline and a simple exercise drinking plan based on your weight, session length and the heat, with an optional sweat test for a personal number.

Enter 0 for a rest day. A one-day cricket match can be 300+ minutes.
Optional: use my sweat test for a personal sweat rate

Weigh yourself in minimal clothing just before and just after a typical session (towel off first). Note what you drank, and any urine you passed. One kilogram of weight lost is about one litre of sweat.

Daily fluid from drinks
0 L
0about 4 hours before training
0during, per hour
0estimated sweat rate

Your plan for this session

When How much Tips
Do not over-drink. Drinking more than you sweat, especially plain water over long sessions, can dilute the sodium in your blood (exercise-associated hyponatraemia), which can be dangerous. If you weigh more after exercise than before, you drank too much. Warning signs include nausea, headache, puffy hands, confusion or unusual tiredness: stop drinking and get medical help. Drinking to thirst, within the range above, protects against both problems.
Check with your doctor if you have kidney disease, heart failure, take diuretics or have been told to limit fluid or salt. Follow their advice over this calculator.

How this hydration calculator works

Daily baseline. The European Food Safety Authority sets an adequate intake of total water of 2.5 litres a day for men and 2.0 litres for women, and the US National Academies set 3.7 litres for men and 2.7 litres for women. These totals include the water in food, which the National Academies estimate at about 20%, so the calculator shows the remaining 80% as your range from drinks. These are for mild climates and moderate activity. You need more on hot days and training days, which is what the session plan adds.

Before training. The American College of Sports Medicine (ACSM) position stand advises drinking about 5–7 ml per kg of body weight at least 4 hours before exercise, plus another 3–5 ml per kg about 2 hours before if you are not passing urine or it is still dark.

During training. The goal is to keep fluid losses under 2% of your body weight, without drinking more than you sweat. The calculator works out your hourly sweat loss (from your sweat test, or estimated from ACSM’s predicted sweat rates for your body weight, effort and a cool or warm climate), then shows the least you need to drink to stay under 2% and the most you should drink, which is your sweat rate. Most athletes end up drinking about 0.4–0.8 litres an hour. The estimate comes from running data, so stop-start sports and gym sessions often sweat less, while long days in strong heat can sweat more: ACSM notes that sweat rates of 0.5 to 2 litres an hour are common in athletes. Your own sweat test beats any estimate.

After training. To recover quickly, drink about 1.25–1.5 litres for every kilogram of body weight you lost, spread over the next few hours, ideally with a meal or salty snack so you hold on to the fluid.

Sodium and long sessions in the heat. Sweat contains sodium (on average about 35 mmol per litre, but anything from 10 to 70). For long sessions, especially in the heat, ACSM notes that drinks with electrolytes and carbohydrate help, and suggests sports drinks with about 20–30 mmol/L of sodium (roughly 460–690 mg per litre). The calculator flags electrolytes for sessions over an hour in the heat or over two hours in any weather. A full day of cricket in the sun is the classic example. Read more in Hydration and electrolytes for men over 35, Cricket fitness after 35 and Why you are always tired after 35.

Sources

  1. European Food Safety Authority (2010), EFSA Journal 8(3):1459: Scientific opinion on dietary reference values for water
  2. US National Academies (2004): Dietary Reference Intakes for water, potassium, sodium, chloride and sulfate
  3. Sawka et al. (2007), Medicine and Science in Sports and Exercise: ACSM position stand on exercise and fluid replacement
  4. Thomas, Erdman and Burke (2016), Journal of the Academy of Nutrition and Dietetics: position of the Academy, Dietitians of Canada and ACSM on nutrition and athletic performance
  5. Hew-Butler et al. (2015), British Journal of Sports Medicine: statement of the 3rd International Exercise-Associated Hyponatremia Consensus Conference

This calculator gives general education, not medical advice. Fluid needs vary a lot between people. Check with your doctor if you have a heart, kidney or blood-pressure condition or take medication that affects fluid or salt balance.

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