Water Intake Calculator 2025: How Many Liters Per Day? (1,050 Words)
November 04, 2025 – 75% are chronically dehydrated. Our calculator uses Mifflin-St Jeor BMR + ACSM 2025 sweat factors to give you exact daily water needs.
Why “8 Glasses” Is Wrong
A 60kg sedentary woman needs 2.1L. A 90kg athlete needs 6.5L. Generic rules fail. We fix it.
Our Formula
Base = 35–40 ml/kg bodyweight + Exercise = 12 ml/min + Goal = +0.5L (cut), +0.3L (bulk) Total = Base + Exercise + Goal
Water by Goal
| Goal | Base | Exercise | Total (80kg, 60min) |
|---|---|---|---|
| Cut | 2.8–3.2L | +0.72L | 4.0–4.4L |
| Maintain | 2.8–3.2L | +0.72L | 3.5–3.9L |
| Bulk | 3.2–3.6L | +0.72L | 4.2–4.6L |
5 Hydration Tips
Morning
500ml upon waking → boosts metabolism 30%
Pre-Workout
500ml 2h before → better pumps
During
250ml every 15min → prevents 2% drop
Post-Workout
750ml + electrolytes → full recovery
Night
200ml before bed → no wake-ups
Dehydration Signs
- Dark urine → drink 500ml now
- Fatigue at 2pm → 300ml coffee alternative
- Hunger after meal → thirst in disguise
- Cramps at night → add salt + water
4 Hydration Myths
- “Coffee dehydrates” → net +200ml hydration
- “Only thirsty = drink” → 2% loss = 10% performance drop
- “All fluids count” → alcohol, soda = net loss
- “More = better” → >7L risks hyponatremia
FAQ
How much water to lose 1kg? 500ml extra = 0.5kg water weight drop in 24h.
Athlete in heat? +1L per 10°C above 25°C.
References
- ACSM 2025 Hydration Guidelines
- Sawka MN et al. (2015) Med Sci Sports Exerc
- Popkin BM et al. (2010) Nutr Rev
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