How much water should
you actually drink?
Skip the vague “8 glasses” rule. Get your personal daily water goal in seconds — from your body, your activity, and your climate.
Fine-tune
Your daily goal
of water a day · about 10.5 glasses or 5 half-litre bottles
- 2.6
- Litres
- 88
- Ounces
- 10.5
- Glasses
Pace yourself
Spread it across the day and ease off after 9:00 PM for better sleep.
Electrolytes? Not needed
For everyday hydration, plain water and a normal diet cover your electrolytes just fine.
A friendly estimate for healthy adults, not medical advice. Your needs rise with heat, exercise, illness, pregnancy, and some medications. Don't drink more than ~1 litre per hour.
Example: a 70 kg moderately active adult in a temperate climate has a daily water goal of about 2.6 litres (88 fluid ounces, roughly 10.5 glasses).
Quick answer
Most adults should drink about 2–3 litres (8–12 cups) of water a day. A good personal target is 30–35 ml per kg of body weight — roughly half an ounce per pound — adding more for exercise, heat, and illness. A 70 kg adult lands near 2.6 litres; this tool fits the number to you.
What shapes your number
Body weight
The foundation — bigger bodies hold and need more water. We start from ~33 ml per kg.
Activity
Every hard hour of training adds fluid lost as sweat, so athletes need noticeably more.
Climate
Heat and humidity push sweat losses up; we add about 10% for hot, humid days.
Life stage & meds
Pregnancy, breastfeeding, and GLP-1 medications all raise your floor.
Frequently asked
How much water should I drink a day?
Most healthy adults need about 2 to 3 litres (roughly 8 to 12 cups) of water a day from drinks. A good personal estimate is 30–35 ml per kilogram of body weight, or about half an ounce per pound, then add more for exercise, heat, pregnancy, or illness.
Is the 8 glasses a day rule accurate?
Eight 250 ml glasses is about 2 litres, which is a fine ballpark for many people — but it isn't based on your size or activity. A 90 kg athlete in the heat needs far more than a 55 kg office worker. That's exactly what this calculator personalises.
Does coffee, tea, and food count toward my water?
Yes. Coffee and tea are mostly water and do count, despite the old 'caffeine dehydrates you' myth. Food provides roughly another 20% of your fluid on top of what you drink, which is why your drinking goal here is a touch lower than your total fluid need.
Can you drink too much water?
Rarely, but yes. Drinking very large amounts very fast can dilute blood sodium (hyponatraemia). Your kidneys clear only about 1 litre per hour, so spread your intake out and don't force far beyond your goal. If you have a kidney or heart condition, ask your doctor.