💧 Water Intake Calculator
Estimate a reasonable daily water intake target based on your body weight, activity level and climate. Individual needs vary — use this as a starting point, not a strict rule.
33 ml per kilogram, plus two allowances
The target is a body-weight rule of thumb with flat additions for training and heat, not a physiological model:
base = kg × 33 ml
sport = 0 / 350 / 700 / 1050 ml (none, 30-60 min, 1-2 h, 2 h+)
heat = 0 / 350 / 700 ml (temperate, warm, hot or humid)At 70 kg the base is 2,310 ml. Add 350 ml for a daily hour of exercise and 350 ml for a warm climate and the target is 3,010 ml - 3.0 L, or 102 fl oz, or 12.7 eight-ounce cups. Pounds are converted at 0.453592 kg first, so 154 lb gives the same figure. The two dropdowns can add at most 1,750 ml between them.
Reading it as a total, not a chore
- Everything you drink counts, including tea, coffee, milk and juice. The mild diuretic effect of caffeine does not cancel out the fluid it came in.
- So does food - fruit, vegetables, soup and yoghurt supply roughly a fifth of most people's intake, so the water you actually pour is less than the figure shown.
- Thirst and urine colour beat arithmetic. Pale straw means you are fine; dark amber means drink. Both respond to today, which no formula does.
Frequently asked questions
How much water should I drink a day?
For a 70 kg adult this works out at about 2.3 L before exercise and climate, and around 3 L with an hour of training in warm weather. Most of it arrives as ordinary drinks and food, not as extra glasses of water.
Does coffee count towards water intake?
Yes. A cup of coffee is mostly water and leaves you net positive on fluid. Only alcohol is genuinely dehydrating at normal serving sizes.
Where did the eight glasses a day rule come from?
A 1945 US recommendation of about 2.5 L a day, which noted in the next sentence that most of it comes from food. The qualifier was dropped and the number stuck.