Example 1 — No exercise
- Weight: 70 kg
- Activity: none
≈ 2.31 L/day
A typical target for a day without much exercise.
Water requirement calculator
Enter your weight and how active you've been today — you'll see roughly how much fluid to aim for.
This is a general guideline, not a fixed prescription. Heat, fever, pregnancy, breastfeeding, and certain health conditions can noticeably change your needs — check with a doctor if you're unsure.
Result
Enter data and click Calculate.
How results are calculated
Water need = weight (kg) × 33 ml + activity add-on.
Water need = header weight (lb) converted to kg × 33 ml/kg + activity add-on.
Add-on: 0 / +350 / +700 ml (none / light / intense or heat).
Rough guide — drink more in heat or heavy sweating.
How to use the calculator
- Enter your weight in the header unit (kg or lb).
- Choose the activity level matching your day.
- Click Calculate to see your daily hydration target.
Usage examples
Example 2 — Light exercise
- Weight: 60 kg
- Activity: light exercise
≈ 2.33 L/day
The extra 350 ml covers fluid lost during a shorter workout.
Example 3 — Intense exercise
- Weight: 90 kg
- Activity: intense exercise / heat
≈ 3.67 L/day
Higher weight plus intense exercise pushes the need up noticeably.
FAQ
How much water should I drink a day?
A common start is about 30–35 ml per kg of body weight, plus extras for training or heat. It's a starting point, not a hard rule.
Does it all have to be plain water?
Soups, tea, coffee, and water in food count too. Plain water is the simplest source — not the only one.
How does exercise change the need?
Longer, harder sessions (and more sweat) mean more fluid. The calculator adds a rough bump for activity.
Do coffee and tea count?
Yes, they count toward fluid balance. With lots of caffeine, some people still add an extra glass of water alongside.
How do I know I'm not drinking enough?
Dark urine, dry mouth, headaches, low energy. Pale yellow urine most of the day usually means you're close.
Can you drink too much water?
Rarely, yes (hyponatremia). Don't force liters “just in case” — drink steadily and match thirst plus context.
Does climate matter?
Heat and humidity raise sweat losses. On hot days, aim higher than in cool weather.
Do older adults need less?
Thirst often fades with age, so dehydration sneaks up. Drink on a schedule, not only when you feel thirsty.