Our calculators

One size never fits all in hydration. Explore our free tools — each one answers a specific question in under a minute.

How it works

1. Tell us about you

Enter your weight, pick your activity level and climate. It takes about 30 seconds — and everything runs in your browser, so your data stays private.

2. Get your number

We calculate your daily target in liters and 8-ounce glasses, and show the full math — baseline, activity adjustment, and climate adjustment — so you know exactly where it comes from.

3. Build the habit

Knowing your target is step one. Use our hydration reminder timer to turn it into a daily routine, and browse the guides to understand the science.

Frequently asked questions

How much water should I drink every day?

It depends on your body weight, activity level, and climate. A solid starting point is 35 ml per kilogram of body weight — for example, about 2.45 liters for a 70 kg adult — plus more if you exercise or spend time in heat. Use the calculator above for your personal number.

Is drinking 8 glasses of water a day enough?

For some people, yes — 8 glasses (about 1.9 liters) covers smaller or sedentary adults. But larger or active people often need 10–13 glasses. Rather than guessing, calculate a target based on your weight.

Do coffee and tea count toward my water intake?

Yes — coffee and tea hydrate you, despite caffeine’s mild diuretic effect. They still count toward daily fluids, but water should be your main source. Keep total caffeine under about 400 mg per day (see our caffeine calculator).

Can you drink too much water?

Yes, though it is rare. Drinking extreme amounts in a short time can dilute blood sodium (hyponatremia). Stick near your calculated target, drink to thirst on top of it, and spread intake through the day.

When do I need electrolytes instead of plain water?

For everyday life and workouts under an hour, plain water is enough. For longer or very sweaty sessions — or hot days outdoors — an electrolyte drink helps replace lost sodium. Read our electrolyte drink guide for details.

How can I remember to drink more water?

Keep water visible (a bottle on your desk), tie drinking to routines (a glass with every meal), and use reminders. Our free hydration reminder timer nudges you at your chosen interval and tracks your glasses.

For information only — not medical advice. If you have a health condition or take medication, ask your doctor how much water is right for you. Read our full disclaimer.