How much water should you drink per day? Your ideal intake depends on your weight, activity, and environment — not a one-size-fits-all "8 glasses."
kg
—L
per day
In glasses (250ml)
—
glasses per day
In fl oz
—
fluid ounces
Per hour (awake)
—
16 waking hours
Base intake (35ml/kg)—
Activity adjustment—
Climate adjustment—
Additional (pregnancy/BF)—
Total daily intake—
Note: This includes water from all sources including food (about 20% of daily intake). Thirst is generally a reliable indicator — if you're thirsty, drink. Urine color is the best hydration indicator: pale yellow = hydrated, dark yellow = drink more.
Hydration — FAQ
Is "8 glasses a day" accurate?
The "8×8" rule (eight 8-oz glasses = 64 oz = ~1.9L) is a rough guideline with limited scientific backing. Your actual needs depend on your size, activity level, climate, and diet. Larger people, athletes, and those in hot climates need significantly more. Smaller people need less.
Does coffee or tea count toward daily water intake?
Yes, mostly. Despite being mildly diuretic, coffee and tea still contribute to overall hydration. Research shows their net diuretic effect is minimal at normal consumption levels. One cup of coffee contributes roughly 80% of its volume to hydration. Alcohol, however, is genuinely dehydrating.
How does dehydration affect sleep?
Even mild dehydration (1–2% of body weight) can impair cognitive function and mood. During sleep, the body loses water through breathing and sweating. Drinking adequate water throughout the day — but not too much right before bed — helps maintain quality sleep without disruptive nighttime bathroom trips.