Daily Water Intake Calculator
Estimate how much water to drink per day based on your weight, activity level, and climate. Returns liters, ounces, and glasses.
What this calculates
Hydration needs vary with body size, activity, and climate. The popular '8 glasses a day' rule is a rough average — actual needs can range from 1.5 to 4 liters daily. This calculator uses a weight-based formula plus adjustments for exercise and hot climates to give a more personalized target.
Formula & how it works
Base intake = 0.033 L per kg of body weight (so a 70 kg adult needs ~2.3 L/day baseline). Add 0.5 L per hour of moderate-to-vigorous exercise. Add 0.5 L in hot/humid climates. Total includes water from food (typically 20 %), so the actual drinking target is the result × 0.8. Coffee and tea count toward intake despite mild diuretic effect.
Worked example
70 kg adult, 1 hour daily exercise, temperate climate. Base = 70 × 0.033 = 2.31 L. Plus exercise = 2.81 L. Drinking target (subtract 20 % from food) = 2.81 × 0.8 = ~2.25 L = ~76 oz = ~9 glasses (8 oz each).
Frequently asked questions
Is too much water dangerous?
Yes, rarely — drinking 4+ liters in a few hours without electrolytes can cause hyponatremia (low sodium). Spread intake throughout the day. The body's natural thirst usually prevents overdrinking.
Do coffee and tea count?
Yes. The diuretic effect of caffeine is mild and well below the fluid you're adding. Same with beer at moderate amounts. Hard liquor is net-dehydrating.
Does urine color matter?
Reasonably useful indicator. Pale straw = well hydrated. Dark yellow = drink more. Clear = possibly overhydrating. Color is affected by B vitamins and some medications, so it's not perfect.
Do I need more during pregnancy or breastfeeding?
Yes — typically 0.3–1 L more per day. The exact amount varies. Listen to thirst and ask your provider.