Water Intake
Daily hydration recommendation
The Water Intake Calculator estimates a daily fluid target from body weight, activity level, and climate. It is a starting point — there is no universally correct "amount of water" for every person, and individual needs vary with diet, medications, and other factors.
The calculator uses the common 35 ml/kg baseline and adjusts upward for higher activity and hotter climates.
What it suggests
- Daily total fluid intake, in litres and US fluid ounces.
- An approximate number of 8 oz glasses to drink.
- Adjustments for exercise and climate.
"Total fluid" includes water, tea, coffee, milk, soup, and water content in food — not just plain water. Most people get 20–30% of their fluid from food (especially fruits, vegetables, and soups).
The estimate
- Baseline: about 35 ml per kg of body weight (≈ 0.5 oz per pound).
- Light exercise: +500 ml.
- Moderate–heavy exercise: +750–1000 ml.
- Hot or humid climate: +500 ml.
Worked example
A 70 kg adult, moderate exercise, temperate climate:
- Baseline =
70 × 35 = 2,450 ml - Plus exercise =
+750 ml - Total ≈ 3.2 litres/day (about 108 fl oz, or ~13 cups).
When this is useful
As a directional daily target — especially helpful for people who notice they consistently drink very little. Athletes during heavy training sessions need additional and more individualized hydration planning (including electrolytes), which this calculator does not cover.
Caveats
Overhydration is possible and in extreme cases dangerous (hyponatremia — diluted sodium levels). Thirst is generally a reliable guide for healthy adults. Some medical conditions (kidney disease, heart failure) require fluid restrictions; speak with a clinician before deliberately increasing intake.
Frequently asked questions
Is it true that I should drink 8 glasses a day?
The "8 × 8" rule is a rough guideline, not an evidence-based prescription. Actual needs vary with body size, activity, and climate.
Does coffee count toward water intake?
Yes. Despite its diuretic effect, caffeinated beverages still contribute net positive fluid in moderate amounts.
What about during exercise?
Add fluid to replace what you lose through sweat. A simple rule: weigh yourself before and after a workout; each kilogram lost is roughly 1 litre of fluid to replace.