Water Intake Calculator
Free daily water intake calculator — how much water to drink per day by weight, gender, activity, and climate. Liters, ounces, and cups.
Everyday Uses
Hot days and heatwaves
Your needs jump in summer — get an adjusted target instead of the generic "8 glasses."
Workout hydration
Know how much extra to drink on training days to replace what you sweat out.
Desk job reminders
Turn your daily target into a bottle count — "3 refills of my 750 ml bottle" — and actually hit it.
Life changes
Pregnancy, breastfeeding, and altitude all change your needs — recalculate instead of guessing.
Frequently Asked Questions
How much water should I drink per day?
Daily water needs vary by body weight, activity, climate, and health. General guidelines: women ~2.7 litres/day total (from all sources), men ~3.7 litres/day (US National Academies). A common formula is 35 ml per kg of body weight — so a 70 kg person needs ~2.45 litres/day from drinks and food. About 20% of daily water comes from food, particularly fruits and vegetables.
Does exercise increase water requirements?
Yes significantly. During exercise, you can lose 0.5–2 litres of sweat per hour depending on intensity, temperature, and individual sweat rate. A practical guide: drink 400–600 ml before exercise, 150–250 ml every 15–20 minutes during, and 450–680 ml for every 0.5 kg of body weight lost during a session. Urine colour is a reliable hydration indicator — pale straw yellow is ideal.
What are the signs of dehydration?
Mild dehydration (1–2% body weight): thirst, dark urine, reduced concentration. Moderate (3–5%): headache, fatigue, dry mouth, reduced physical performance. Severe (>5%): rapid heartbeat, confusion, dizziness, fainting. Even mild dehydration impairs cognitive performance by 5–10% and reduces endurance exercise capacity. You are often mildly dehydrated before you feel thirsty.
Does coffee and tea count toward daily water intake?
Yes. Despite mild diuretic effects, caffeinated drinks like coffee and tea are net hydrating at typical consumption levels (1–4 cups/day). Studies show that moderate caffeine intake does not increase net fluid loss. Milk, juice, herbal teas, and even water-rich foods like cucumber, watermelon, and soup all count toward your daily fluid intake.
Can you drink too much water?
Yes — overhydration (hyponatremia) occurs when you drink so much water that sodium levels in the blood become dangerously low. Risk is highest for endurance athletes who drink large amounts of plain water during long events (>4 hours). Symptoms include nausea, headache, confusion, and in severe cases seizures. For healthy adults in normal conditions, the kidneys can process up to ~1 litre per hour, making overhydration from drinking very rare.