Water Intake Calculator
Estimate a daily drinking-water target from your weight, exercise time and climate. Thirst and pale-yellow urine are still your best everyday guides.
An estimate of drinking water. Thirst and pale-yellow urine are your best day-to-day guides. Kidney or heart conditions change the target - ask your doctor.
How the estimate works
Water = 33 ml x kg + 500 ml per hour of exercise + 500 ml if hot/humid
This is drinking-water guidance. Total water needs (per the Institute of Medicine) are around 3.7 L/day for men and 2.7 L/day for women including the roughly 20% you get from food.
Source: general hydration guidance; IOM adequate intake reference.
Frequently asked questions
Does coffee count toward hydration?
Mostly yes. In normal amounts, coffee and tea are net hydrating despite mild diuretic effects. Water is still the simplest choice.
Can you drink too much water?
Yes. Drinking far more than you need can dilute blood sodium (hyponatremia), which is dangerous. Match intake to thirst and activity rather than forcing liters.
Where does the 8x8 rule come from?
The 8 cups a day idea is a rough guideline, not a strict rule. Real needs vary with size, activity, climate and diet, which is why we factor those in.
How much extra do I need when exercising?
Roughly 500 ml per hour of exercise is a reasonable starting estimate, more in heat. Drink to thirst and check urine color.
Medical disclaimer: This calculator is for general information and education only. It is an estimate, not medical advice, diagnosis or treatment. Always talk to your doctor or midwife about your health and any decisions.