Water Intake Calculator
Estimate your daily water needs from weight, exercise, and climate.
Enter your values and calculate to see the result.
Formula used
base = weight(kg) × 35 ml
exercise = (minutes ÷ 30) × 500 ml
total = (base + exercise) × (hot climate ? 1.1 : 1)
litres = total ÷ 1000
cups = total ÷ 250
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Worked example
70 kg, 30 min exercise/day, temperate climate:
Base = 70 × 35 = 2,450 ml
Exercise = (30 ÷ 30) × 500 = 500 ml
Total = 2,450 + 500 = 2,950 ml ≈ 2.95 L (about 12 cups).
Frequently asked questions
Is this the same as total fluid intake?
It estimates plain water from weight and activity. Other drinks and water-rich foods count toward overall hydration, but this tool focuses on water itself.
Why does exercise increase my water need?
You lose fluid through sweat and breathing during activity. The calculator adds about 500 ml for every 30 minutes of exercise to replace what you lose.
Does hot weather really change the number?
Yes — heat raises sweat losses. The calculator adds about 10% when you select a hot climate.
Can I drink too much water?
Yes, in rare cases. Very high intake can dilute sodium (hyponatremia). The estimate here is a sensible daily target, not a maximum; drink to thirst as well.
Should children or athletes use a different rule?
This formula suits most adults. Children, older adults, and heavy endurance athletes have different needs — follow guidance from a clinician or sports dietitian.