How much water do you actually need?
Forget "8 glasses a day." Your real need depends on weight, activity, climate, caffeine, and life stage. Calculated using the Institute of Medicine baseline plus published adjustments.
Why personal hydration matters
Even 2% dehydration drops physical performance, concentration, and mood. Chronic mild dehydration is linked to kidney stones, urinary tract infections, headaches, and constipation. This calculator personalises your daily target using six real inputs.
01
Body + activity
Weight, exercise level, life stage.
02
Environment
Climate, caffeine intake — both shift fluid loss measurably.
03
Live check
Urine-colour wheel to validate the target against your body in real time.
Formula: Institute of Medicine Dietary Reference Intakes for Water (2005). Urine-colour reference: Armstrong LE et al. Int J Sport Nutr Exerc Metab. 1998;8:345-355. This is an educational estimator, not medical advice. People with heart failure, kidney disease, or on diuretics should follow their physician's specific fluid prescription.