Water Needs Calculator

How much water should you drink per day?

Adequate water intake is one of the basic prerequisites for health. Water participates in almost all body functions: it transports nutrients, regulates temperature, lubricates joints, and helps in metabolism. But how much water do you actually need?

How is water need calculated?

The general recommendation is about 33 milliliters per kilogram of body weight per day. This is a baseline estimate for an adult doing sedentary or light work. Exercise, hot climate, and other factors increase the need.

Our calculator uses the formula:

Water need = Weight (kg) × 33 ml × Activity factor

Activity factors

Why is adequate drinking important?

Mild dehydration (1–2% of body weight) can already cause:

• Fatigue and decreased concentration
• Headache
• Slowed metabolism
• Decreased performance in exercise
• Dry skin

When do you need more water?

• During sports performances – drinking before, during, and after exercise
• In hot weather – sweating increases fluid loss
• When sauna bathing – you can lose up to half a liter of fluid in the sauna
• When sick – especially with fever, vomiting, or diarrhea
• During pregnancy and breastfeeding – water need increases significantly

Tips for adequate drinking

1. Keep a water bottle with you – a visible water bottle reminds you to drink
2. Drink evenly throughout the day – don't try to drink everything at once
3. Start the day with a glass of water – the body dehydrates during the night
4. Use a reminder app – many apps remind you to drink
5. Eat water-rich foods – cucumber, watermelon, tomato contain a lot of water

Remember: not just plain water

Daily fluid intake also includes other drinks (tea, coffee, juice) and water in food. About 20–30% of daily fluid comes from food.

Sources:

• CDC – Water and Healthier Drinks
• Mayo Clinic – Water: How much should you drink every day?
• NIH – Drinking Water and Healthy Hydration