Calculate your daily intake.
Enter your details below for a personalized calculation including a full 8-slot daily schedule.
STEP 01
Your profile.
Gender
Activity Level
Climate / Temperature
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Your personalized hydration result will appear here.
How much water per day — the science.
The 8×8 rule — and why it's outdated
The popular "8 glasses per day" rule has no specific scientific origin. A 2002 review in the American Journal of Physiology found no evidence supporting this one-size-fits-all guideline. Individual needs vary by up to 300% based on body size, activity, and environment.
What the science actually says
The Institute of Medicine recommends an adequate intake (AI) of 3.7 liters per day for men and 2.7 liters per day for women — but this includes water from all food and beverages. Plain water accounts for about 20% of intake from food alone, so the drinking target is roughly 3.0L for men and 2.2L for women as a baseline.
The formula we use
Our calculator uses a weight-based formula adjusted for gender: Weight (kg) × 33ml for men, Weight (kg) × 31ml for women. This is then multiplied by activity and climate factors, with additional exercise bonuses (+500ml per 30 min). This approach is endorsed by multiple sports medicine organizations.
Daily water intake by body weight
| Weight | Men (L/day) | Women (L/day) | Cups (avg) |
|---|---|---|---|
| 50 kg (110 lbs) | 1.6L | 1.5L | ~6–7 |
| 60 kg (132 lbs) | 2.0L | 1.9L | ~8 |
| 70 kg (154 lbs) | 2.3L | 2.2L | ~9 |
| 80 kg (176 lbs) | 2.6L | 2.5L | ~10–11 |
| 90 kg (198 lbs) | 3.0L | 2.8L | ~12 |
| 100 kg (220 lbs) | 3.3L | 3.1L | ~13 |
* Baseline figures for moderate activity in temperate climate. Add 10–35% for heat, and 500ml per 30 min of exercise.
FAQ — daily intake.
Follow the ACSM protocol: drink 400–600ml (14–22 oz) 2 hours before exercise, 150–350ml (5–12 oz) every 15–20 minutes during exercise, and 1.5× the fluid lost after exercise (roughly 750ml per pound of body weight lost). Our water intake calculator during exercise adds 500ml per 30 minutes of daily workout time to your baseline recommendation.
For exercise under 60 minutes at moderate intensity, plain water is sufficient. For longer sessions, high-intensity workouts, or exercise in heat, sports drinks with electrolytes (sodium, potassium, magnesium) help replace sweat losses and prevent hyponatremia. The rule of thumb: water for workouts under 60 minutes, electrolytes for anything longer or in hot conditions.
During a marathon, aim for 500–750ml per hour. Avoid drinking only plain water for runs over 90 minutes — add sodium via electrolytes to prevent hyponatremia. Weigh yourself before and after your long run; aim to lose no more than 2–3% of body weight. Pre-race: drink 500ml 2 hours before the start, then 150–250ml at the start line.
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