Free calculator
Water intake calculator
How much to drink in a day from your weight, plus what today's training adds. Worked out in your browser; nothing is sent anywhere.
Work out your water
Fluid today
—a day
- From your weight
- —
- Training adds
- —
Enter your weight to see your number.
How it works
A day's fluid, from water and every other non-alcoholic drink, is 35 ml for every kg you weigh (about half a fluid ounce a pound), rounded to the nearest 50 ml. That sits within the European Food Safety Authority's adequate intakes: a 70 kg adult's 2.45 L is between EFSA's 2.0 L for women and 2.5 L for men.
Base = 35 ml × weight (kg)
Training: sweat = 0.5 (easy) · 0.9 (moderate) · 1.2 (hard) L an hour; during, drink the middle of 0.4 L an hour and your sweat rate (at most 0.8 L); after, 1.25 × the sweat still lost
The sweat rates sit inside the American College of Sports Medicine's range of 0.3–2.4 L an hour, and replacing 1.25 times what's still lost after a session follows the National Athletic Trainers' Association. Heat, humidity and your own body change real sweat a lot; a weigh-in before and after a session shows yours.
- EFSA Panel on Dietetic Products, Nutrition and Allergies (2010). Scientific opinion on dietary reference values for water. EFSA Journal, 8(3), 1459. doi.org/10.2903/j.efsa.2010.1459
- Sawka MN, Burke LM, Eichner ER, et al. (2007). Exercise and fluid replacement (ACSM position stand). Medicine & Science in Sports & Exercise, 39(2), 377–390. pubmed.ncbi.nlm.nih.gov
- McDermott BP, Anderson SA, Armstrong LE, et al. (2017). National Athletic Trainers' Association position statement: fluid replacement for the physically active. Journal of Athletic Training, 52(9), 877–895. nata.org
Questions
How much water should I drink a day?
About 35 ml for every kg of body weight, from all your drinks: 2.45 L (83 fl oz) for a 70 kg (154 lb) adult. Training days ask for more, to replace the sweat.
Do coffee, tea and milk count?
Yes. Every non-alcoholic drink counts toward the day's fluid, and food brings some water on top. Water is still the easiest choice for most of it.
How much should I drink when I exercise?
During a session, about 0.4–0.8 L an hour for most adults, and never more than you sweat. Afterwards, drink about 1.25–1.5 L for every kg of body weight still lost. In heat, or past two hours of hard sweating, salt matters too.
Can I drink too much water?
Yes. Drinking far more than you sweat, especially during long events, can dilute the salt in your blood. That's why the during-exercise amount is capped at what you sweat. If you have heart or kidney disease or have been told to limit fluids, follow your doctor's advice instead.
Fullday tracks this for you every day.
Its fluid target uses this same rule and adds each finished workout's sweat for you. Coming to the App Store this December, free to download.
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