How much water should you drink a day? It depends mostly on your body weight and how active you are. Enter yours below for a personalized daily target in litres and cups.
A general estimate (≈33 mL per kg, adjusted for activity). It includes fluid from food and other drinks. Needs rise in heat, illness, pregnancy, and breastfeeding. Thirst and pale-yellow urine are good day-to-day guides. Ask your doctor if you have heart or kidney conditions.
How Much Water Do You Really Need?
A common rule of thumb is about 33 mL of fluid per kilogram of body weight per day, before adjusting for activity, climate, and health. For a 70 kg adult that’s roughly 2.3 litres — but that total includes the water in food, tea, coffee, and other drinks, not just plain water.
| Body weight | Light activity | Very active |
|---|---|---|
| 50 kg | ~1.7 L | ~2.4 L |
| 70 kg | ~2.3 L | ~3.0 L |
| 90 kg | ~3.0 L | ~3.7 L |
Signs You May Need More Water
Thirst is the obvious one, but also watch for dark-yellow urine, headaches, fatigue, and dizziness. Dehydration develops faster in children, older adults, and during illness — see our guide on dehydration in children. Staying hydrated also supports a healthier heart.
Frequently Asked Questions
Is 8 glasses of water a day a real rule? “8×8” (eight 8-oz glasses) is a rough, easy-to-remember target — about 2 litres. It’s reasonable for many adults but not based on strict science. Your real needs depend on weight, activity, and climate.
Does coffee and tea count toward hydration? Yes. Despite the myth, moderate caffeinated drinks still contribute to your daily fluid intake. Water and milk are better default choices, and water is calorie-free.
Can you drink too much water? Rarely, but yes — drinking extreme amounts in a short time can dangerously dilute blood sodium (hyponatremia). Spread intake through the day and let thirst guide you.