Staying hydrated supports performance, focus, digestion and recovery. But 'drink 8 glasses' is a one-size-fits-all rule — your real needs depend on your body, activity and climate.
How the estimate works
We start from roughly 35 ml per kilogram of bodyweight, then add fluid for training (0.5–1.5 L) and hot or humid conditions (0.5 L). This covers total water; about a fifth normally comes from food.
Listen to your body
Thirst is a reliable signal for most healthy people, and urine colour is an easy check. Use the calculated number as a planning target, not a rigid quota.
Frequently asked questions
A common target is about 35 ml per kg of bodyweight — roughly 2.5–3.5 litres for most adults — increased for exercise and hot weather. Thirst and urine colour are good real-time guides.
The '8×8' rule (about 2 litres) is a reasonable baseline for an average sedentary adult, but larger, more active people in hot climates need more.
Yes, though it's rare. Drinking well beyond your needs — especially during long endurance events without electrolytes — can dangerously dilute blood sodium (hyponatremia).