Hydration Calculator How Much Water You Need Daily
Enter your weight, activity level, climate, and caffeine intake to get your personalised daily water target — plus a timeline and glass tracker.
Your Inputs
Adjust the fields below, then click Calculate.
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millilitres of water per day
— oz | — litres
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Base intake (ml)
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Activity add-on (ml)
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Climate add-on (ml)
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Caffeine offset (ml)
When to Drink — Daily Timeline
Progress Tracker — Glass Counter
250 ml per glass. Tap a glass to fill it.0 / 0 glasses
About This Calculator
How daily water targets are calculated.
Base intake is calculated at 35 ml per kg of body weight for sedentary adults, a value supported by EFSA (European Food Safety Authority) guidelines.
Activity multiplier adds 300–700 ml depending on intensity, reflecting average sweat losses during moderate to intense training.
Climate factor adds up to 600 ml in extreme heat to compensate for increased perspiration and respiratory losses.
Caffeine offset adds a small compensatory volume (~150 ml per 200 mg caffeine) because caffeine has a mild diuretic effect, though caffeinated drinks still contribute positively to overall hydration.
Exercise add-on is calculated at 500 ml per 30 minutes of exercise and is shown separately in the breakdown.
Frequently Asked Questions
Evidence-based hydration guidance.
How much water should I drink per day?
General guidelines recommend about 35 ml of water per kilogram of body weight per day for sedentary adults in a temperate climate. A 70 kg (154 lb) adult would need approximately 2.5 litres (84 oz). However, actual needs vary with activity level, heat exposure, and diet. Athletes training for more than 1 hour per day may need an additional 500–1000 ml. This calculator accounts for all those factors.
Does caffeine make you dehydrated?
Moderate caffeine consumption (up to 400 mg per day, or roughly 4 cups of coffee) has a mild diuretic effect but does not cause net fluid loss in habitual coffee drinkers. Research shows that caffeinated beverages still contribute to daily hydration. This calculator adds a small compensatory amount (roughly 150 ml per 200 mg caffeine) to account for increased urine output, not because coffee is dehydrating per se.
How do I know if I am dehydrated?
The most reliable everyday indicator of hydration status is urine colour. Pale yellow (like lemonade) indicates good hydration. Dark yellow or amber suggests mild to moderate dehydration. Clear urine may indicate overhydration. Other signs of dehydration include headache, reduced concentration, dry mouth, and reduced energy. Thirst is a late indicator — do not wait until you feel thirsty to drink.
How much extra water do I need when exercising?
A practical rule is to drink 500 ml (17 oz) of water for every 30 minutes of moderate exercise, or up to 750 ml per 30 minutes during intense exercise in the heat. Weigh yourself before and after a workout: every 1 kg of weight lost corresponds to approximately 1 litre of fluid lost. Aim to replace 125–150% of that deficit within 4–6 hours of finishing exercise.
Can I drink too much water?
Yes. Hyponatraemia (dangerously low blood sodium) can occur when extremely large volumes of water are consumed without electrolyte replacement — typically more than 1 litre per hour over several hours, most commonly seen in endurance athletes. For most people, exceeding their daily target by 500–1000 ml is harmless and simply increases urination. Electrolyte drinks or sodium-containing foods are advisable for exercise lasting more than 90 minutes to prevent dilutional hyponatraemia.