Water Intake CalculatorHow Much Water Should I Drink a Day?
Get a personal daily water target in ounces, litres and cups, based on your weight, exercise, weather and pregnancy, plus an hour-by-hour drinking schedule and a tap-to-log glass tracker.
Built & medically reviewed by Manzoor Ahmad, Pharmacist & Calculator Developer · Updated
Benchmarked against the National Academies water DRIs and ACSM exercise fluid guidance.
How much water should you drink a day?
Women need about 2.2 L (74 oz, about 9 cups) and men about 3.0 L (101 oz, about 13 cups) from drinks each day. A more personal estimate is 30 mL per kg of body weight (about ½ oz per lb), plus roughly 0.7 L per hour of exercise and 0.5–1 L in hot weather. Pale straw-coloured urine means you’re drinking enough.
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That’s 2.3 litres, or about 10 cups (8 oz each), from drinks.
Total water including food: about 2.9 L
Tap a glass each time you drink
0 of 10 glasses
Your hydration schedule
How much water should you drink a day? (Official guidance)
The National Academies set “adequate intakes” for total water from all drinks and food. About 80% usually comes from drinks.
| Group | Total water / day | From drinks (~80%) | In cups (8 oz) |
|---|---|---|---|
| Men 19+ | 3.7 L (125 oz) | 3.0 L (101 oz) | ≈ 13 cups |
| Women 19+ | 2.7 L (91 oz) | 2.2 L (74 oz) | ≈ 9 cups |
| Pregnant | 3.0 L (101 oz) | 2.3 L (78 oz) | ≈ 10 cups |
| Breastfeeding | 3.8 L (128 oz) | 3.1 L (105 oz) | ≈ 13 cups |
| Teens 14–18 (boys / girls) | 3.3 / 2.3 L | 2.6 / 1.8 L | ≈ 11 / 8 cups |
How we estimate your water needs
Instead of the old “8 glasses a day” rule, we start from your body weight and add what you lose through sweat and heat. The result is a drinks target, because your food already supplies about a fifth of your water.
143 lb (65 kg) woman, 30 min workout, mild weather
- Baseline: 65 × 30 = 1,950 mL
- Exercise: 30 × 12 = 360 mL
- Drinks target: 2,310 mL ≈ 78 oz ≈ 10 cups
- Total water including food: 2,310 ÷ 0.8 ≈ 2.9 L, slightly above the NASEM 2.7 L for women because of her workout.
- On a hot day, add 0.5 L to reach about 95 oz.
Urine colour: your simplest hydration gauge
possibly too much
well hydrated ✓
fine
drink soon
dehydrated
Some vitamins (B2/riboflavin), beetroot and medicines such as rifampicin, phenazopyridine and nitrofurantoin change urine colour regardless of how much you drink. Don’t use colour alone if you take them.
When “drink more water” is the wrong advice
Some people are on a fluid restriction, often 1.5–2 L a day, and must not follow general targets. These include people with heart failure, advanced kidney disease, liver cirrhosis with fluid build-up, and SIADH. Follow your cardiologist’s or nephrologist’s limit.
Other medicines make hydration more important. With lithium, dehydration can push blood levels into the toxic range. SGLT2 inhibitors (dapagliflozin, empagliflozin) and diuretics increase fluid loss. Metformin users should hold doses during severe vomiting or diarrhoea. Ask your pharmacist about “sick day rules”.
Older adults lose their sense of thirst, so scheduled drinks, like the timetable above, work better than waiting until they’re thirsty.
8 easy ways to drink more water
- Drink a full glass as soon as you wake up.
- Keep a marked bottle at your desk.
- Have a glass before every meal. It also helps with appetite.
- Use the glass tracker above. Logging works.
- Flavour water with citrus, mint or cucumber.
- Count tea, coffee and milk. Moderate caffeine still hydrates.
- Eat water-rich foods: watermelon, cucumber, oranges, soups.
- Stop about 90 minutes before bed so you don’t wake up at night.
Related calculators
Water Intake calculator FAQs
Most women need about 2.2 L (74 oz, about 9 cups) and most men about 3.0 L (101 oz, about 13 cups) from drinks each day, according to the National Academies. A weight-based estimate is about 30 mL per kg (0.5 oz per lb), plus extra for exercise and hot weather.
A good everyday estimate is 30 mL per kg of body weight, or about half an ounce per pound. A 150 lb (68 kg) person needs about 2 litres (68–75 oz) from drinks before adding exercise or heat.
Eight 8 oz glasses (64 oz, 1.9 L) is close to right for many smaller adults on a mild day. It’s usually too little for larger or active people, and in hot weather. Your weight and sweat losses are better guides.
Yes. Coffee and tea at normal intakes (up to about 3–4 cups a day) hydrate you nearly as well as water. Caffeine’s mild diuretic effect is mostly offset by the fluid in the drink. Milk, juice and soups count too.
Drink about 400–800 mL (14–27 oz) per hour of exercise, depending on how much you sweat. Weighing yourself before and after training helps: drink about 1.25–1.5 L for every kilogram you lose. For sessions over 60–90 minutes, add electrolytes.
Yes. Drinking very large amounts quickly, more than about 1 L per hour for several hours, can dilute blood sodium (hyponatremia). This causes headache, confusion, and in severe cases seizures. Endurance athletes and people taking MDMA or some antidepressants are most at risk.
The National Academies recommend about 3.0 L of total water a day during pregnancy (about 2.3 L, or 10 cups, from drinks), and 3.8 L while breastfeeding (about 3.1 L from drinks).
Early signs include thirst, dark yellow urine, dry mouth, headache and tiredness. Severe dehydration causes dizziness, a fast heartbeat, confusion and very little urine, and needs medical attention, especially in children and older adults.
A small glass is fine, but finish most of your fluids about 90 minutes before bed to avoid waking up to use the bathroom. That’s why the schedule above stops early.
Manzoor Ahmad
Pharmacist · Supplement & Nutrition Writer (9+ yrs) · Calculator Developer (13+ yrs)
I’m a practising pharmacist and I build DexoCalc’s calculators. Hydration questions come up at my counter every day, from people on lithium and diuretics to people with heart failure on fluid limits. So this calculator gives a personal target, and it also tells you when you shouldn’t follow it.
References
- National Academies. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate (2005).
- American College of Sports Medicine. Exercise and fluid replacement position stand. Med Sci Sports Exerc. 2007;39(2):377–390. PubMed
- EFSA Panel. Scientific Opinion on Dietary Reference Values for water. EFSA Journal. 2010;8(3):1459. EFSA
- Killer SC, et al. No evidence of dehydration with moderate daily coffee intake. PLoS One. 2014;9(1):e84154. PubMed
- CDC. About Water and Healthier Drinks.
Medical disclaimer: These targets are for healthy adults and are not medical advice. If you have heart failure, kidney or liver disease, or are on a fluid restriction or medicines such as lithium or diuretics, follow your doctor’s fluid advice instead.