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- Water Intake Calculator: How Much Water Should You Drink?
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Water Intake Calculator: How Much Water Should You Drink?
This water intake calculator gives you a daily fluid target in litres and 250 ml glasses, based on your body weight, exercise and climate, and shows how much of it is extra for training. It is a practical starting point for healthy adults.
Journals that use this number
Every number calculated by code from published formulas.
- Walking plan for weight lossfrom €15Enter your current steps, height, weight, age, goal and how long you can walk. Your journal sets a weekly step ramp, picks interval or incline sessions to suit your knees and kit, and estimates the distance and energy behind every target.
- Ramadan training & nutrition planfrom €17Your journal sets calories, protein, meal split and water from your body and goal, then fits your sessions around the time you can actually train, with a daily log for all 30 days of fasting.
- GLP-1 muscle-protection planfrom €19Your journal turns your height, weight, appetite and training set-up into a daily protein number, a per-meal target and a 12-week strength plan you tick off week by week, alongside your prescriber's care.
How it's calculated
The baseline is 33 ml per kilogram of body weight, a common rule of thumb for adult fluid needs. On top of that it adds 0.35 L for every 30 minutes of exercise a day, and another 0.5 L if you live or train in a hot or humid climate. The total is then converted into 250 ml glasses, rounded to the nearest glass.
The figure covers what you drink. Food typically supplies a meaningful share of your water on top of that (roughly 20% for many diets), more if you eat a lot of fruit, vegetables and soups. Tea, coffee, milk and other drinks all count towards your total; moderate caffeine does not cancel out the fluid it comes with.
Sweat losses vary widely between people. The exercise allowance is an average; heavy sweaters, long sessions and hot conditions can need considerably more. For sessions longer than about an hour, or if you see salt marks on your clothes, include electrolytes (especially sodium) rather than only plain water. Drinking large volumes of plain water during long endurance events can dangerously lower blood sodium.
The simplest check is your urine: pale straw colour usually means you are well hydrated, while dark yellow suggests you need more. Thirst is a reliable guide for most healthy adults, but it becomes less sensitive with age, so older adults benefit from drinking on a routine. Spread intake through the day rather than drinking it all at once.
Important: if you have kidney disease, heart failure, liver disease or have been told to limit fluids, follow your doctor's advice rather than this calculator. Some medications also change fluid needs. Hydration matters when appetite is low, for example on GLP-1 medication; see the GLP-1 muscle plan. If you are walking daily, the walking plan for weight loss builds in a routine, and the calorie calculator sets your energy needs.
| Body weight | Water per day | 250 ml glasses | With 30 min exercise |
|---|---|---|---|
| 50 kg | 1.7 L | ≈ 7 | 2.0 L |
| 60 kg | 2.0 L | ≈ 8 | 2.3 L |
| 70 kg | 2.3 L | ≈ 9 | 2.7 L |
| 80 kg | 2.6 L | ≈ 11 | 3.0 L |
| 90 kg | 3.0 L | ≈ 12 | 3.3 L |
| 100 kg | 3.3 L | ≈ 13 | 3.7 L |
Frequently asked questions
How much water should I drink a day?
Most healthy adults need roughly 30–35 ml of fluid per kilogram of body weight a day from drinks, which is about 2–3 litres for many people. Add more for exercise, hot weather and illness with fever. Food provides extra water on top of this. Pale yellow urine and rarely feeling thirsty are good signs that you are drinking enough.
Is 8 glasses of water a day enough?
Eight 250 ml glasses is 2 litres, which is close to enough for many smaller or less active adults, but too little for larger or very active people and those in hot climates. It is a memorable rule, not a scientific one. Your weight, activity and environment change your needs, which is why a personalised estimate is more useful.
Does coffee or tea count towards water intake?
Yes. Tea, coffee, milk and other drinks all count towards your daily fluid intake. Caffeine has a mild diuretic effect, but in moderate amounts the fluid in the drink more than makes up for it, especially if you drink coffee regularly. Sugary drinks and alcohol count as fluid too, but bring calories and other downsides.
How much water should I drink when exercising?
A useful starting point is about 0.35 L for every 30 minutes of exercise, on top of your normal intake, with more in heat. Drink before you start, sip during longer sessions and rehydrate afterwards. Weighing yourself before and after training shows your sweat loss: each kilogram lost is roughly one litre of fluid to replace.
Can you drink too much water?
Yes. Drinking very large amounts of plain water in a short time can dilute the sodium in your blood, a condition called hyponatraemia, which can be dangerous. It is rare in daily life but more likely during long endurance events. Drink to thirst, include electrolytes in long or hot sessions, and avoid forcing down large volumes quickly.
What are the signs of dehydration?
Common signs include thirst, dark yellow urine, urinating less often, headache, tiredness, dizziness and dry mouth. During exercise you may notice your heart rate rising more than usual for the same effort. Severe dehydration, with confusion, fainting or no urine for many hours, needs urgent medical attention, especially in children and older adults.
Does drinking more water help with weight loss?
Water itself does not burn fat, but it can help indirectly. Replacing sugary drinks with water cuts calories, and drinking a glass before meals may help some people feel fuller. Staying hydrated also makes training feel easier. For actual fat loss, your calorie balance still decides the outcome; water supports the habits that create it.
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- Calorie Calculator: Your Maintenance Calories (TDEE)
- Macro Calculator: Protein, Carbs and Fat for Your Goal
- Heart Rate Zone Calculator: Find Your Zone 2 and All Five Zones
- Body Fat Calculator: US Navy Tape-Measure Method
- Protein Calculator: How Much Protein Do You Need?
- BMI Calculator with Waist-to-Height Ratio
General fitness information, not medical advice. Check with a doctor if you have a medical condition, are pregnant or have an injury.