Water Intake Calculator
Calculate how much water you should drink a day from your weight, exercise and climate — daily target in litres and 250 ml glasses.
About the Water Intake Calculator
How much water should you drink a day? This water intake calculator gives a personalised answer from three inputs: your body weight, how many minutes you exercise daily, and your climate. It returns a daily target in litres and as a count of standard 250 ml glasses, so the number is easy to act on.
The estimate starts from a widely used baseline of about 33 ml of water per kilogram of body weight — roughly 2.3 litres for a 70 kg adult. It then adds around 350 ml for every 30 minutes of exercise to replace sweat losses, plus a climate adjustment of 500–750 ml for hot or very hot and humid conditions where you lose more fluid even at rest.
Remember that all fluids and even food count towards hydration — roughly 20% of daily water typically comes from meals. Your needs also rise during pregnancy, breastfeeding and illness. Rather than forcing an exact number, use the target as a guide and let pale-yellow urine and rare thirst confirm you are drinking enough.
How to Use the Water Intake Calculator
- 1Enter your body weight in kilograms.
- 2Enter your average daily exercise in minutes.
- 3Select your climate — temperate, hot, or very hot and humid.
- 4Read your daily water target in litres and 250 ml glasses.
Frequently Asked Questions
How much water should I drink a day?
A common evidence-informed baseline is about 33 ml per kilogram of body weight — around 2.3 L for a 70 kg person — plus extra for exercise and heat. Official adequate-intake figures (including all beverages and food moisture) are about 3.7 L per day for men and 2.7 L for women, so plain-water targets of 2–3 L suit most adults.
Is the '8 glasses a day' rule accurate?
It is a reasonable rough average but not personal. Eight 250 ml glasses is 2 litres — close to the baseline for a 60 kg adult, too little for a heavier person who trains in the heat, and more than a small sedentary person strictly needs. Weight-based formulas like the one used here scale the target to your body and lifestyle.
How much extra water do I need when exercising?
A practical rule is roughly 350 ml of additional water per 30 minutes of moderate exercise, which is what this calculator adds. Heavy sweaters, long sessions and hot conditions can push losses to 1–2 litres per hour, in which case weighing yourself before and after training (drink about 1.5 L per kg lost) gives a more precise replacement target.
Do tea, coffee and food count towards my water intake?
Yes. Despite caffeine's mild diuretic effect, tea and coffee still contribute net fluid, and food supplies about 20% of most people's water — fruit and vegetables can be over 90% water. Your calculated target is total fluid; you do not need to hit it with plain water alone, though water is the best zero-calorie default.
Can you drink too much water?
Yes — drinking many litres in a short window can dilute blood sodium (hyponatremia), which is dangerous. It is rare in normal life but documented in endurance events where athletes overdrink. Spread intake through the day, do not force fluids far beyond your target, and prioritise electrolyte replacement during very long, sweaty efforts.