How the water intake calculator works
This calculator uses a common baseline of roughly 35ml of water per kilogram of body weight, then adds a fixed adjustment for exercise-related fluid loss and hot/humid climates:
Base intake (ml) = Weight (kg) × 35
Total = Base + Activity adjustment + Climate adjustment
Total = Base + Activity adjustment + Climate adjustment
Step-by-step guide
- Enter your body weight.
- Select how physically active you typically are in a week.
- Select whether you're usually in a hot/humid climate.
- Read your estimated daily water intake in litres and glasses.
Signs you might not be drinking enough
Dark yellow urine, persistent thirst, fatigue and headaches can all signal mild dehydration. Pale yellow urine is a commonly used rough indicator of adequate hydration for most healthy adults.
Frequently asked questions
It's a reasonable rough starting point for many people, but individual needs vary meaningfully with body size, activity, climate and diet — this calculator gives a more personalized estimate than the flat 8-glass rule.
No — this estimates fluid you should drink. Food (especially fruits and vegetables) typically contributes roughly 20% of total daily water intake on top of what you drink.
Yes — thirst is a reliable day-to-day signal for most healthy adults. Use this calculator as a general planning guide, not a hard limit, and increase intake during illness, pregnancy, or breastfeeding as advised by a healthcare provider.