Daily Water Intake Calculator
Free daily water intake calculator — estimate how much water to drink each day from your body weight and activity level. Works in your browser.
Type your body weight and how much exercise you’ll do today. The calculator returns an estimated daily water target.
The formula
base = weight (kg) × mL per kg (commonly 30–40 mL/kg) activity bonus = (exercise minutes ÷ 60) × hourly sweat estimate
We add the two for a daily total. The default mL/kg is 35, the middle of the typical adult range.
Activity bonus
Sweat rate varies a lot, but rough hourly estimates:
| Intensity | mL per hour active |
|---|---|
| Light (no real sweat) | 0 |
| Moderate (light sweat) | ~350 |
| Intense (heavy sweat) | ~700 |
In a hot, humid climate add another 50–100% to the activity bonus.
What counts as fluid
All of it. Plain water, milk, tea, coffee, juice, soup, and the water in fruit and vegetables. The clinical literature counts total fluid intake, not just water from the tap. Coffee and modest alcohol still contribute net fluid despite a mild diuretic effect.
Not medical advice
This is a baseline estimate. People with heart, kidney or liver conditions, or on specific medications, may need different intake — talk to your doctor.
Worked examples
-
70 kg, no exercise → ~2.45 L
Drink about 2,450 mL (2.45 L) per day.
-
70 kg + 60 min moderate exercise → 2.8 L
Drink about 2,800 mL (2.8 L) per day.
Frequently asked questions
Where does the 35 mL/kg rule come from?
It's a long-standing nutrition rule of thumb — roughly 30–40 mL per kg of body weight per day for a typical adult. 35 is a reasonable middle. For comparison, the "8 cups a day" advice (8 × 240 mL = 1.92 L) lands close for a smaller adult; bigger / more active people need more.
Does the water need to be plain water?
No. Total daily fluid intake includes water, milk, juice, coffee, tea, and the water content of food (fruit, vegetables, soup). Plain water is the cleanest, but other drinks count too. Caffeine and alcohol have mild diuretic effects but at typical doses they still contribute net fluid.
What if I'm pregnant, breastfeeding or in a hot climate?
Higher than average. Pregnancy adds ~300 mL/day, lactation ~700 mL/day, and hot or humid climates can dramatically increase sweat loss. Use this as a baseline and adjust upward.
Can I drink too much water?
Yes — drinking very large amounts very quickly can cause **hyponatremia** (dilutional low blood sodium). It's rare for someone drinking to thirst, but real for long endurance events and certain medical conditions. Spread intake across the day; don't chug litres at a time.
This isn't medical advice, right?
Correct. If you have heart, kidney or other medical conditions that restrict fluid, follow your doctor's instructions instead.
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