Water Intake Calculator
How much water should you actually drink each day? Enter your weight in metric (kg) or imperial (lb) units, plus your activity level, and get a personalized daily target in liters or cups.
Water intake
Estimate your daily water intake from weight and activity.
FAQs
Is 8 glasses of water a day really the rule?
Eight 8-oz glasses (about 2 liters) is a decent average, but needs vary a lot with weight, activity, and climate. A personalized estimate based on your weight is more useful than a one-size number.
Can I drink too much water?
Yes, though it is rare. Drinking far more than you need in a short time can dilute blood sodium (hyponatremia). Stick near your calculated target, drink to thirst on top of it, and spread intake through the day.
How it works
A common baseline is about 35 ml of water per kilogram of body weight. For example, a 70 kg person needs roughly 70 × 35 = 2,450 ml, or about 2.5 liters per day.
In imperial terms that works out to roughly half an ounce per pound: a 160 lb person needs about 80 oz, or around 10 cups. Active people and hot climates push the target higher — add about 500 ml (2 cups) per hour of exercise.
Select your activity level in the calculator and it adjusts the target for you. Remember that food contributes water too (fruits, vegetables, soups), so the target is a guide, not a quota to force down.
Why the "8 glasses" rule is only a starting point
The 8-glasses guideline assumes an average adult and average conditions. A 55 kg office worker and a 95 kg construction worker in summer heat have very different needs, which is why a weight-based estimate beats a flat rule.
Use the flat rule as a floor, not a ceiling. If you are larger, active, or somewhere warm, your real target is higher.
Activity changes everything
An hour of hard exercise can cost you 500 ml to over a liter of sweat. That is why the calculator asks about activity level — sedentary and very active people can differ by a liter or more per day.
A simple habit: drink a glass before and after workouts, and keep water visible during the day. Most shortfalls come from forgetting, not from needing exotic hydration strategies.
Signs you are getting it right
Pale yellow urine, steady energy through the afternoon, and rarely feeling very thirsty are all good signs. Dark urine, headaches, and dry mouth suggest you are running behind.
Do not chase a number obsessively — adjust up on hot or active days, ease off when you are less active, and let the calculator's target be your anchor.