How Much Water Should You Drink Per Day? (By Body Weight)
How much water should you drink a day? Enter your weight to get your target in liters, fl oz, and cups. Uses the 35 ml/kg baseline (NAM) plus add-ons for exercise, hot climate, pregnancy, and breastfeeding — with a quick-reference chart.
See step-by-step calculation
The NAM Adequate Intake (AI) — the level assumed sufficient for nearly all healthy people — is 3.7 L/day (~125 oz) for men and 2.7 L/day (~91 oz) for women, but roughly 20% of that comes from food. Individual sweat rate matters more than any formula: outdoor athletes in heat can lose up to 1.5 L per hour, while a sedentary office worker in AC barely cracks 500 ml of insensible loss. Use the result as a daily target, not a prescription.
When to use this calculator
- Athlete planning training-day fluid intake (baseline + 12–16 oz per training hour, electrolytes >60 min)
- Post-illness rehydration after fever, vomiting, or diarrhea (add 500 mL per °F above 100.4°F)
- Pregnancy hydration target per NAM (+300–500 mL above non-pregnant AI; ~3.0 L total water/day)
- Kidney stone prevention per AUA guideline (aim for 2.5+ L urine output, often 3+ L total fluid intake)
- Breastfeeding mothers producing ~750 mL milk/day (+700 mL fluid above baseline)
- Outdoor workers in hot climates tracking heat-stress hydration
- Older adults with diminished thirst sensation setting structured fluid reminders
- Weight-loss clients replacing caloric beverages with water
Water content of common foods (the ~20% you don't have to drink)
The NAM Adequate Intake assumes roughly 20% of daily water comes from food. These percentages (USDA FoodData Central) show why a salad-and-fruit-heavy day quietly covers 300–800 mL of your target. The 'water per typical serving' column converts the percentage into millilitres so you can subtract it from the number this calculator gives you.
| Food | Water content | Typical serving | Water per serving |
|---|---|---|---|
| Cucumber | 95% | 1 cup sliced (119 g) | ~113 mL |
| Iceberg lettuce | 96% | 2 cups shredded (110 g) | ~106 mL |
| Celery | 95% | 1 cup chopped (101 g) | ~96 mL |
| Watermelon | 92% | 1 cup diced (152 g) | ~140 mL |
| Tomato | 94% | 1 medium (123 g) | ~116 mL |
| Strawberries | 91% | 1 cup halved (152 g) | ~138 mL |
| Cantaloupe | 90% | 1 cup diced (160 g) | ~144 mL |
| Spinach (raw) | 91% | 2 cups (60 g) | ~55 mL |
| Broth-based soup | ≈92% | 1 bowl (245 g) | ~225 mL |
| Orange | 87% | 1 medium (131 g) | ~114 mL |
| Plain yogurt | 85% | 1 cup (245 g) | ~208 mL |
| Cooked oatmeal | 84% | 1 cup (234 g) | ~197 mL |
Percentages are approximate USDA FoodData Central values for raw/cooked foods and vary by ripeness and preparation. Coffee, tea, milk and juice also count toward fluid intake (Beverage Hydration Index, AJCN 2016) — only alcohol has a net dehydrating effect at higher doses.
NAM Adequate Intake for total water, by age and sex
The National Academies of Medicine set these Adequate Intake (AI) values for TOTAL water — beverages plus food. They are population targets, not personal prescriptions; the calculator above scales by your body weight, which is usually a closer fit for an individual.
| Group | Total water AI (L/day) | ≈ fl oz/day | ≈ 8 oz cups/day |
|---|---|---|---|
| Boys 9–13 | 2.4 | 81 | 10 |
| Girls 9–13 | 2.1 | 71 | 9 |
| Boys 14–18 | 3.3 | 112 | 14 |
| Girls 14–18 | 2.3 | 78 | 10 |
| Men 19+ | 3.7 | 125 | 16 |
| Women 19+ | 2.7 | 91 | 11 |
| Pregnancy (14–50) | 3.0 | 101 | 13 |
| Lactation (14–50) | 3.8 | 128 | 16 |
Source: National Academies of Medicine, Dietary Reference Intakes for Water (2005). About 20% of these totals normally comes from food, so the beverage-only target is roughly 80% of the figures shown.
How it works
Quick-reference table: daily water by body weight
The baseline formula is 35 ml × weight in kg (or 0.5 fl oz × weight in lb). The table below shows sedentary intake in a temperate climate (no exercise, no climate or pregnancy add-ons):
| Weight (lb) | Weight (kg) | Liters/day | Fl oz/day | Cups/day |
|---|---|---|---|---|
| 110 lb | 50 kg | 1.75 L | 59 oz | ~7.4 cups |
| 130 lb | 59 kg | 2.07 L | 70 oz | ~8.7 cups |
| 150 lb | 68 kg | 2.38 L | 80 oz | ~10 cups |
| 154 lb | 70 kg | 2.45 L | 83 oz | ~10.4 cups |
| 175 lb | 79 kg | 2.77 L | 94 oz | ~11.7 cups |
| 200 lb | 91 kg | 3.19 L | 108 oz | ~13.5 cups |
| 220 lb | 100 kg | 3.50 L | 118 oz | ~14.8 cups |
| 250 lb | 113 kg | 3.97 L | 134 oz | ~16.7 cups |
Add-ons on top of the base: +600 ml per hour of exercise · +500 ml for hot/humid climate · +500 ml if pregnant · +700 ml if breastfeeding.
NAM Dietary Reference Intakes: the actual numbers
The National Academies of Medicine (NAM) Adequate Intake (AI) — the level assumed to meet the needs of nearly all healthy people:
| Group | Total water AI | From beverages | From food |
|---|---|---|---|
| Men 19+ | 3.7 L/day (~125 oz) | 3.0 L (~13 cups) | 0.7 L (~24 oz) |
| Women 19+ | 2.7 L/day (~91 oz) | 2.2 L (~9 cups) | 0.5 L (~17 oz) |
| Pregnancy | 3.0 L/day | 2.3 L | 0.7 L |
| Lactation | 3.8 L/day | 3.1 L | 0.7 L |
About 20% of daily water comes from food — watermelon is 92% water, cucumber 95%, soup ~90%, leafy greens 90+%, yogurt ~85%. So a man hitting the NAM AI by drinking 13 cups of pure water and eating a typical mixed diet is technically over-target.
Does coffee dehydrate you? No.
Maughan's 2016 Beverage Hydration Index meta-analysis (American Journal of Clinical Nutrition) ranked drinks by 2-hour fluid retention vs. still water. Milk, oral rehydration solution, and orange juice scored higher than plain water; coffee and tea scored essentially equal to water at typical serving sizes (~3 mg/kg caffeine). The diuretic effect of caffeine is real but small and offset by the fluid volume of the beverage. Bottom line: coffee, tea, milk, juice, and even diet soda count toward the AI for healthy adults.
The 0.5–1 oz per lb rule explained
The rule has no formal endorsement, but it cross-checks well against NAM. A 200 lb active man → 100–200 oz → 3.0–5.9 L, which spans the NAM AI (3.7 L) plus exercise replacement. For sedentary adults, 0.5 oz/lb is enough; 1 oz/lb is reserved for hard-training athletes, hot climates, or large body sizes. Use it as a sanity check, not gospel.
Athlete protocols: Galpin baseline + ACSM electrolytes
Andy Galpin's working protocol for athletes: 0.5 oz × body weight in lb as baseline, then 12–16 oz of fluid per hour of training. The American College of Sports Medicine Position Stand on Exercise and Fluid Replacement adds the electrolyte layer — for sessions over 60 minutes, replace sodium 500–700 mg/L, potassium 80–200 mg/L of fluid. Sweat sodium concentration ranges 600–1,200 mg/L (heavy salty sweaters trend higher), potassium 200–700 mg/L, magnesium 100–300 mg/L. Plain water for >1 hour endurance without electrolytes is the classic setup for exercise-associated hyponatremia (serum Na <135 mmol/L) — rare but potentially fatal. Marathon runners drinking >1 L/hour of pure water are the textbook case.
Hydration assessment: WUT and urine color
Three simple field markers (the WUT check):
Urine specific gravity (USG) <1.020 is the lab-grade marker of euhydration; >1.030 signals dehydration.
Clinical exceptions — when more isn't better
Thirst, urine color, and how you feel during the day are still the best real-time gauges. The number this calculator gives you is a starting target — adjust based on what your body tells you.
Frequently asked questions
How much water should I drink per day based on my weight?
Is the '8 glasses a day' rule accurate?
Does coffee count toward my daily water intake?
What does healthy urine color look like?
Do I need to drink extra water when exercising?
How much water should pregnant women drink per day?
Do foods like watermelon and cucumber count as water intake?
When should I use a sports drink instead of plain water?
Can drinking too much water be dangerous?
How much water should older adults drink?
How much water should I drink to help prevent kidney stones?
Sources & references
- Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate — National Academies of Medicine — National Academies of Sciences, Engineering, and Medicine (NAM) (2005)
- Exercise and Fluid Replacement — ACSM Position Stand — American College of Sports Medicine, Medicine & Science in Sports & Exercise (2007)
- A randomized trial to assess the potential of different beverages to affect hydration status (Beverage Hydration Index) — Maughan et al. — American Journal of Clinical Nutrition (2016)
- Medical Management of Kidney Stones: AUA Guideline — American Urological Association (AUA) (2014 (amended 2019))
- Reduced thirst after water deprivation in healthy elderly men — Phillips et al. — New England Journal of Medicine (1984)
- Nutrition During Pregnancy — ACOG FAQ — American College of Obstetricians and Gynecologists (2023)
Methodology & trust
Calculadora de salud revisada por el equipo editorial de Hacé Cuentas, contrastada con Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate — National Academies of Medicine, según nuestra política editorial y metodología.
Última revisión: June 22, 2026. Los parámetros se verifican periódicamente con las fuentes citadas.
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Indicative results. For critical decisions, consult a professional.
Rodríguez, M. (2026). How Much Water Should You Drink Per Day? (By Body Weight). Hacé Cuentas. https://hacecuentas.com/daily-water-intake-by-weight-calculator
Contenido bajo licencia CC-BY 4.0 — reutilizable citando la fuente con enlace a Hacé Cuentas.