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    Water Intake Calculator

    Calculate your recommended daily water intake based on your weight, activity level, and climate.

    Free to use. Runs in your browser.

    Enter your weight and activity level to see recommended daily water intake. The general guideline is 30 to 35 ml per kg body weight, increased for exercise, hot weather, and pregnancy.

    Calculate Your Daily Water Intake

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    How Much Water Do You Really Need? (It's Not 8 Glasses)

    The "8 glasses a day" rule is one of the most repeated health myths in history. No one knows where it came from, and no scientific study supports it as a universal recommendation. The truth is simpler and more individual: your water needs depend on your body size, activity level, climate, and diet.

    A 50 kg sedentary woman in a cool climate needs far less water than a 90 kg man running in summer heat. A blanket recommendation of "2 litres" is meaningless without context. This calculator gives you a personalised estimate based on factors that actually matter.

    That said, most people don't drink enough. A 2015 study in Nutrition Reviews found that roughly 75% of adults are in a state of mild chronic dehydration, not enough to cause obvious symptoms, but enough to affect concentration, mood, and physical performance.

    Daily Water Intake by Body Weight

    As a baseline, most experts recommend 30 to 35 ml of water per kilogram of body weight per day for moderately active adults. Exercise, heat, and altitude increase this.

    Body WeightSedentaryModerately ActiveVery Active / Hot Climate
    55 kg / 121 lbs1.7 L2.0 L2.5 L
    70 kg / 154 lbs2.1 L2.5 L3.2 L
    85 kg / 187 lbs2.6 L3.0 L3.8 L
    100 kg / 220 lbs3.0 L3.5 L4.5 L

    What this means for you: An 85 kg person who exercises moderately needs about 3 litres per day. That's roughly 12 cups. Some of this comes from food (fruits, vegetables, soups contribute 500 to 700 ml daily), so your actual drinking target is closer to 2.3 to 2.5 litres from fluids.

    Signs You're Not Drinking Enough

    Mild dehydration (1 to 3% fluid loss) doesn't always cause obvious thirst. By the time you feel thirsty, you're already dehydrated. Watch for these subtler signs:

    Physical Signs

    • Dark yellow urine, aim for pale straw colour
    • Headaches, especially in the afternoon
    • Dry mouth and lips
    • Reduced exercise performance, just 2% dehydration can cut performance by 10 to 20%
    • Constipation

    Mental Signs

    • Difficulty concentrating
    • Irritability or mood changes
    • Fatigue, sometimes mistaken for lack of sleep
    • Feeling hungry when you shouldn't be, the brain often confuses thirst and hunger signals

    The urine test is the simplest check. Pale straw = well hydrated. Dark yellow = drink more. Completely clear = you might be overhydrating (yes, that's possible too).

    Does Coffee Count? What About Tea and Juice?

    Yes, coffee and tea count. Despite the myth, caffeine at normal doses (up to 400 mg/day, about 4 cups of coffee) doesn't cause net dehydration. A 2014 study in PLOS ONE found that coffee in moderate amounts hydrates just as effectively as water.

    Here's how common drinks compare:

    DrinkHydration ValueNotes
    Water100%The gold standard
    Herbal tea~100%Counts fully, no caffeine concerns
    Coffee/black tea~95%Mild diuretic effect at high doses, but still a net positive
    Milk~110%Actually more hydrating than water due to electrolytes and fat
    Fruit juice~90%Hydrating, but high in sugar and calories
    Alcohol (beer)~60%Mild diuretic, you retain about 60% of the fluid
    Alcohol (spirits)~20%Strong diuretic, causes net fluid loss

    Hydration for Exercise

    Your water needs increase significantly during exercise. A good framework:

    • Before exercise: Drink 400 to 600 ml (2 cups) 2 to 3 hours before training
    • During exercise: 150 to 250 ml (about 1 cup) every 15 to 20 minutes
    • After exercise: Replace 150% of fluid lost, weigh yourself before and after training; drink 1.5 litres for every kg lost
    • For sessions over 60 minutes: Add electrolytes (sodium, potassium) through sports drinks or electrolyte tablets

    Use our Calories Burned Calculator to estimate your exercise intensity, which directly correlates with fluid loss.

    Related Health Tools

    Calorie CalculatorFind your daily calorie needsMacro CalculatorPlan your protein, carbs, and fatCalories BurnedSee how exercise affects hydration needsBMI CalculatorCheck your Body Mass IndexTDEE CalculatorCalculate your total energy expenditureWeight Loss CalculatorPlan your weight loss timeline

    Part of a workflow

    Health & Fitness Workflow

    Body baseline → Calories → Nutrition → Training → Progress. 13 tools free.

    How to use this tool

    1

    Select your preferred unit system (Imperial or Metric)

    2

    Enter your age and gender

    3

    Input your current weight

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    Frequently Asked Questions

    How much water should I drink per day?
    It depends on your weight, activity, and climate. As a baseline, 30 to 35 ml per kg of body weight works for most adults. An 80 kg person needs roughly 2.4 to 2.8 litres per day. This calculator gives a personalised estimate based on your specific factors.
    Does coffee or tea count towards water intake?
    Yes. A 2014 study in PLOS ONE found that coffee hydrates just as effectively as water at moderate intake (up to 4 cups). Tea, milk, and juice all count too. Only alcohol at higher concentrations (spirits) causes net fluid loss.
    How does exercise affect water needs?
    You lose 500 to 1,500 ml of sweat per hour of exercise depending on intensity and temperature. Drink 150 to 250 ml every 15 to 20 minutes during exercise, and replace 150% of fluid lost afterwards. Weigh yourself before and after training, drink 1.5 litres for every kg lost.
    Can I drink too much water?
    Yes. Hyponatraemia (water intoxication) occurs when excessive water intake dilutes blood sodium levels. It's rare in everyday life but can happen during endurance events. Signs include nausea, headache, and confusion. If your urine is completely clear, you may be overhydrating.
    Does climate affect water intake needs?
    Significantly. Hot, humid weather can double your fluid needs through increased sweating. Cold, dry air (especially heated indoor air in winter) also causes dehydration through respiratory water loss. Altitude above 2,500m increases water needs by 200 to 500 ml per day.
    What colour should my urine be?
    Pale straw (light yellow) means well hydrated. Dark yellow or amber means you need more fluids. Completely clear may mean you're drinking too much. First-morning urine is always darker, judge hydration from mid-day samples.
    Does drinking water help with weight loss?
    Indirectly, yes. A study in Obesity found that drinking 500 ml of water before meals led to 44% more weight loss over 12 weeks. Water has zero calories, replaces sugary drinks, and can reduce appetite. It also supports metabolic function during a calorie deficit.
    How much water do children need?
    Children aged 4 to 8 need about 1.2 litres per day. Ages 9 to 13 need 1.6 to 1.8 litres. Teenagers need 1.8 to 2.6 litres depending on sex and activity. These estimates are from the European Food Safety Authority. Active kids in hot weather need more.
    Is sparkling water as hydrating as still water?
    Yes. Carbonated water hydrates identically to still water. The only difference is that carbonation can make you feel full faster, which may cause some people to drink slightly less. The myth that sparkling water is dehydrating has no scientific basis.
    Should I drink water even if I'm not thirsty?
    For most adults under 65, thirst is a reliable guide, drink when you feel like it. For older adults (65+), the thirst mechanism weakens with age, so proactive hydration becomes more important. Athletes should also drink on a schedule during exercise rather than relying on thirst.
    Does food contribute to water intake?
    Yes, about 20% of daily water intake comes from food. Fruits and vegetables are especially hydrating: watermelon (92% water), cucumber (95%), oranges (87%), and yoghurt (88%). A diet rich in whole foods naturally boosts hydration.
    How does pregnancy affect water needs?
    Pregnant women need roughly 300 ml more per day than usual (about 2.3 litres total). Breastfeeding women need an extra 700 ml (about 2.7 litres total). Dehydration during pregnancy can reduce amniotic fluid and trigger contractions. Always consult your midwife for specific guidance.

    Results are for general informational purposes only and should be checked before use. They are not professional advice. See our Disclaimer and Terms of Service.