How much water should I drink a day?

A practical starting point is about 35 ml of water per kilogram of body weight — roughly 2.4 litres (around 10 glasses) for a 70 kg adult — then add about 350 ml for every 30 minutes of exercise and 10% more in a hot or humid climate. Rather than the flat "drink 2 litres" rule that ignores your size and activity, this calculator works out a personalised daily total and shows it in litres, glasses (250 ml) and bottles (500 ml), with a sensible range because needs vary day to day.

How many ounces of water should I drink a day?

In US units, the same 35 ml/kg guideline works out to roughly 0.5 fl oz of water per pound of body weight before adjustments — about 83 fl oz (a little over 10 cups) for a 154 lb / 70 kg adult, rising with exercise and heat. That lines up with the common "eight 8-oz glasses (64 oz)" rule of thumb as a floor, with most active adults landing closer to 80–110 oz a day. The calculator shows your personal figure in fluid ounces and cups alongside litres, glasses and bottles, so you can use whichever unit you think in.

How much water should I drink based on my weight?

Body weight is the single biggest driver of fluid need, because a bigger body has more cells and a larger surface area losing water. A common guide is 30–40 ml per kg of body weight; this calculator uses 35 ml/kg as a middle estimate. That works out to roughly 1.8 litres for a 50 kg person, 2.5 litres for a 70 kg person, and 3.5 litres for a 100 kg person before any adjustment for exercise or heat.

Does exercise change how much water I need?

Yes — you lose fluid through sweat, so the longer and harder you train the more you need to replace. This calculator adds about 350 ml of water for every 30 minutes of exercise on top of your baseline, which is why an active day lands well above a sedentary one. For long or intense sessions, especially in the heat, you may also need electrolytes (sodium) alongside the extra water.

Should I drink more water in hot weather?

Yes. In hot or humid conditions you sweat more even at rest, so your fluid losses rise. This calculator lifts your whole daily total by 10% when you select a hot climate. On very hot days, during travel to a hot country, or with a fever, you may need more again — let thirst, and the colour of your urine (pale straw is the target), guide you.

Can drinking water help with weight loss?

Indirectly, yes. Water has zero calories, and drinking a glass before a meal increases fullness so you tend to eat a little less — studies on "pre-loading" with water show a small but real reduction in calorie intake. Thirst is also easy to mistake for hunger, so staying hydrated can cut unnecessary snacking. And swapping sugary drinks or juice for water removes liquid calories that are easy to over-consume. Water is not a fat-burner on its own; it helps by supporting appetite control and replacing higher-calorie drinks.

Does the water have to be plain water, or do other drinks count?

Other drinks count. Tea, coffee, milk, and juice are mostly water and all contribute to your daily total — the old idea that caffeine is so dehydrating it cancels out the fluid is a myth at normal intakes. Food matters too: fruit, vegetables and soups provide roughly 20% of most people's fluid, which is why you don't need to literally drink every millilitre of the figure above. For weight loss, though, plain or unsweetened drinks are best so you aren't adding calories.

Can you drink too much water?

Yes, though it is uncommon. Drinking a very large volume in a short time can dilute blood sodium (hyponatraemia), which is dangerous — this is mainly a risk for endurance athletes who over-drink during long events. For everyday life, spreading your intake across the day and letting thirst guide you keeps you safely within range. People with heart, kidney or liver conditions should follow the fluid target their doctor sets rather than a general calculator.

Hydration

Daily Water Intake Calculator — Free

Work out how much water to drink per day from your body weight, how long you exercise and your climate — in litres, glasses, bottles and fluid ounces, not a one-size-fits-all 2 litres.

Water Intake Calculator

Gender

Required: fluid needs and pregnancy/breastfeeding guidance differ by biological sex (male or female).

Age

Range: 15–100 years.

Weight (kg)

Range: 30–300 kg · bigger bodies need more water

Exercise (minutes / day)

Range: 0–600 minutes · adds 350 ml per 30 min for sweat losses.

Exercise intensity (optional)

Scales the sweat add-on for how hard you sweat. Moderate ≈ 350 ml / 30 min.

Climate

Mild or air-conditioned conditions. A hot climate adds 10%.

*This calculator is for informational purposes only. Please consult a healthcare professional before making any health decisions. See our medical disclaimer for more information.

Quick Answer

How Much Water Should You Drink Per Day?

This free water intake calculator sets your daily water target from your body weight — about 35 ml per kg, or roughly 2.4 litres (10 glasses, ~83 fl oz) for a 70 kg / 154 lb adult — then adds 350 ml for every 30 minutes of exercise and 10% more in a hot climate. Instead of the flat "drink 2 litres" rule, it gives you a personalised total in litres, glasses (250 ml), bottles (500 ml), and US fluid ounces / cups, with a sensible range. Enter your details above to get your number.

Daily Water Intake by Body Weight

Your size is the biggest factor in how much water you need — which is exactly what the "2 litres for everyone" rule ignores. The table below shows a temperate-climate baseline (35 ml/kg) next to an active day with 60 minutes of exercise added. A hot climate would lift each figure by a further 10%.

Body weight	Sedentary day	Active day (+60 min)
50 kg (110 lb)	1.8 L	2.5 L
70 kg (154 lb)	2.5 L	3.2 L
90 kg (198 lb)	3.2 L	3.9 L
110 kg (243 lb)	3.9 L	4.6 L

These are total fluid targets — remember that food and other drinks supply roughly 20% of it, so you don't need to drink the whole figure as plain water.

Adjusting for Exercise and Climate

Exercise: sweat is mostly water, so every workout adds to your needs. This calculator adds about 350 ml for each 30 minutes of moderate exercise — so a 45-minute session adds roughly 525 ml, and 90 minutes adds just over a litre. Because sweat rate varies, you can set the session intensity: a light, barely-sweating session adds less, while a hard, dripping session adds more. For long or sweaty sessions, pair the extra water with some sodium (a pinch of salt, an electrolyte tab, or salty food) so you actually hold on to what you drink.

Climate: in a hot or humid environment you lose more fluid through sweating and breathing even before you move, so the calculator raises your whole total by 10%. Air-conditioned offices and mild weather sit in the temperate band; a heatwave, a hot-country holiday, or a fever can push you above even the hot-climate figure. The colour of your urine is the simplest real-time check — aim for pale straw, not dark yellow.

Water Intake Calculator for Weight Loss

Using a water intake calculator for weight loss isn't about a magic number — hydration won't melt fat, but it makes a calorie deficit easier to stick to in three ways. First, water fills you up: drinking a glass or two before a meal stretches the stomach and reliably lowers how much you eat at that meal. Second, the body can confuse thirst with hunger — staying topped up cuts the mild "am I hungry?" signals that lead to snacking. Third, swapping fizzy drinks, juice and sweetened coffees for water removes liquid calories, which are some of the easiest to over-consume because they don't fill you up.

The practical move: get most of your target in before and between meals, and reach for water first when you feel peckish. Then build the rest of your plan — set your calorie budget with the TDEE Calculator, choose a sensible deficit, and lock in protein to stay full with the Protein Intake Calculator.

Hitting Your Target Through the Day

Front-load the morning. A glass on waking and one with breakfast clears a big chunk of your total before the day gets busy.
Anchor water to meals and your commute. A bottle with each meal and a refill at your desk makes the target automatic instead of something to remember.
Drink to your workout. Add the exercise portion around training — some before, sips during, the rest after.
Check the colour. Pale-straw urine means you're on track; dark yellow means top up. Ease off in the last hour or two before bed to protect your sleep.

Water Intake Calculator — Limitations

⚠This is general hydration guidance for healthy adults, not a medical fluid prescription — individual needs vary with diet, sweat rate, medication and air conditioning.
⚠It estimates total fluid; food and other drinks supply roughly 20% of it, so you do not need to drink the whole figure as plain water.
⚠Very long or intense exercise, especially in heat, also needs electrolytes (sodium) — water alone may not be enough to stay balanced.
⚠People with heart, kidney or liver conditions, or anyone on fluid-restricting medication, should follow the target their doctor sets, not a general calculator.
⚠If you are pregnant or breastfeeding your needs are higher — follow your midwife or doctor's advice.

Safe Execution Protocol: Water Intake Next Steps

Before you start drinking to this target, a few practical guidelines keep your hydration safe and effective:

Spread your intake across the day rather than drinking a large volume all at once.
Add the exercise portion around your training — some before, sips during, the rest after.
In hot weather or for long sessions, pair extra water with sodium (electrolytes or salty food).
Use urine colour as your real-time guide — pale straw is the target, dark yellow means top up.
If you have a heart, kidney or liver condition, follow the fluid target your clinician sets instead.

Use the clinical routing dashboard below to execute these steps safely with verified professional resources.

CDC Assessment Guide

Precision Tracking Tools

Monitor your baseline metrics with clinical accuracy to ensure you stay on target.

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U.S. Dietary Guidelines

Custom Meal Design

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Academy of Nutrition

Expert Coaching

Connect with certified professionals who can tailor strategies to your unique physiology.

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Scientific References

Institute of Medicine (U.S.) Panel on Dietary Reference Intakes for Electrolytes and Water. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC: National Academies Press; 2005. (source of the ~20% of fluid from food and the adult adequate-intake figures.) National Academies Press
EFSA Panel on Dietetic Products, Nutrition, and Allergies (NDA). Scientific Opinion on Dietary Reference Values for water. EFSA Journal. 2010;8(3):1459. EFSA
Sawka MN, et al. American College of Sports Medicine position stand: Exercise and fluid replacement. Med Sci Sports Exerc. 2007;39(2):377–90. PubMed
Dennis EA, et al. Water consumption increases weight loss during a hypocaloric diet intervention in middle-aged and older adults. Obesity (Silver Spring). 2010;18(2):300–7. PubMed

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