About this tool
There's no single scientifically "correct" number for how much water a person needs each day — hydration science spans a range of institutional guidances (bodies like the U.S. National Academies and the European Food Safety Authority land on somewhat different totals, and most build in a wide margin because individual needs vary hugely by body size, activity, climate, and health status). What many everyday hydration calculators converge on, though, is a simple starting heuristic: roughly 35 mL of water per kilogram of body weight per day. It's not a prescription — just a widely-cited rule of thumb that scales sensibly with body size.
This calculator applies that baseline and then layers on the adjustments that move the number in real life: it adds roughly 12 mL per minute of exercise to help replace sweat losses (capped at a reasonable ceiling), 500 mL in hot or humid conditions, and 300 mL for pregnancy or 700 mL for breastfeeding when either applies. The result appears in liters, milliliters, US fluid ounces, and 250 mL "glasses", plus a quick 500 mL bottle-count for a gut check. Treat the number as a reasonable starting estimate rather than a strict target — thirst itself is a good everyday signal for most healthy adults, and anyone managing a kidney, heart, or other condition that affects fluid balance should get personalized guidance from a clinician instead of a web calculator.
Frequently asked questions
Does coffee or tea count toward my daily water intake?
Generally yes — modern research has largely walked back the older belief that caffeinated drinks are strongly dehydrating; in moderate amounts, coffee and tea do still contribute net fluid to your daily total. That said, this calculator's target is meant primarily as a plain-water guideline, since water has no calories, sugar, or caffeine-related side effects (sleep disruption, mild diuretic effect at high doses) to worry about.
Is drinking too much water dangerous?
Yes, in extreme cases — drinking far more water than your kidneys can process (a condition called hyponatremia, or water intoxication) dangerously dilutes blood sodium levels, though this typically only happens from drinking very large volumes in a short period, often in endurance-sports or extreme-challenge contexts, not from normal daily hydration habits. This calculator's estimates are well within safe everyday ranges — if you have kidney, heart, or liver conditions affecting fluid balance, follow your doctor's specific guidance instead of a general calculator.