A general daily water intake guideline based on your body weight.
Baseline ≈ 35ml per kg of body weight, with an addition for exercise. This is a general wellness guideline, not a personalized medical recommendation.
For general wellness information only — not medical advice. Consult a healthcare professional for personal guidance.
The "8 glasses a day" figure is one of the most widely repeated health rules with the weakest evidence behind it. Its roots trace to a 1941 US Food and Nutrition Board recommendation of roughly 2.5 litres a day, worked out at about 1 millilitre of fluid per calorie of food eaten — but that same 1941 report went on to note that most of that quantity is already contained in ordinary food, a detail that got dropped as the "8 glasses" version spread. Since food (especially fruits, vegetables and soups) and other beverages like tea and coffee all count toward hydration, treating "8 glasses of plain water" as a separate, additional requirement overstates what's actually needed for most people.
More recent guidance from the US National Academies puts total daily fluid intake (from all sources, not water alone) at roughly 2.7 litres for women and 3.7 litres for men in a temperate climate — figures that already include water obtained from food. There is genuinely no single number that fits everyone: heat, exercise intensity, altitude, pregnancy, breastfeeding and individual health conditions all shift real fluid needs meaningfully, which is why this calculator's output is a starting reference point to adjust from, not a fixed daily prescription. A simple practical check that works for most healthy adults: pale yellow urine generally indicates adequate hydration, while consistently dark urine is a more useful day-to-day signal than counting glasses.
It traces back to a 1941 US Food and Nutrition Board recommendation of about 2.5 litres of fluid daily, based on roughly 1ml per calorie consumed. Crucially, that same report noted most of that amount is already contained in ordinary food — a caveat that got lost as the simplified "8 glasses" version spread through popular health advice.
Yes. Fruits, vegetables, soups, tea, coffee and other beverages all contribute to total hydration, not just plain water. Treating "8 glasses of water" as an amount separate from everything else you eat and drink significantly overstates most people's real additional water need.
The US National Academies' guidance is roughly 2.7 litres of total fluid a day for women and 3.7 litres for men in a temperate climate — and this figure already includes fluid from food, not just water drunk directly. Individual needs shift meaningfully with heat, exercise, altitude, pregnancy and health conditions.
Urine colour is a practical everyday signal for most healthy adults — pale yellow generally indicates adequate hydration, while consistently dark yellow suggests you may need more fluids. It's not diagnostic on its own, but it's a more responsive daily check than counting a fixed number of glasses.