Water Intake Calculator
Find out exactly how much water you should drink each day — based on your body weight, activity level, and climate. Get results in litres, glasses, and 500 ml bottles.
Daily Water Needs at a Glance
| Body Weight | Base (35 ml/kg) | Active (+500 ml) | Hot + Active (+1250 ml) |
|---|---|---|---|
| 55 kg | 1.9 L | 2.4 L | 3.2 L |
| 70 kg | 2.5 L | 3.0 L | 3.8 L |
| 85 kg | 3.0 L | 3.5 L | 4.3 L |
| 100 kg | 3.5 L | 4.0 L | 4.8 L |
Frequently Asked Questions
How much water should I drink per day?
A common guideline is 35 ml per kg of body weight per day — approximately 2.5–3.5 L for most adults. The exact amount varies with activity level, climate, diet, and individual physiology. Sedentary adults in a cool climate need less; athletes in hot weather need significantly more. This calculator accounts for activity and climate adjustments on top of the weight-based baseline.
Does the '8 glasses a day' rule hold up?
The '8 × 8 rule' (8 glasses of 8 oz = 64 oz ≈ 1.9 L) is a rough average that works for small, sedentary adults in mild climates. It has no scientific basis as a universal recommendation. Actual needs range from 1.5–4+ L per day depending on body size, activity, and environment. The weight-based approach (35 ml/kg) is more individualised.
Does coffee or tea count toward daily water intake?
Yes — coffee and tea contribute to daily fluid intake. While caffeine is a mild diuretic, the net fluid contribution of caffeinated drinks is still positive. A coffee drinker does not need to 'replace' the coffee with extra water. Alcohol, however, is a stronger diuretic and increases fluid needs — drink water alongside alcoholic beverages.
How do I know if I'm drinking enough water?
Urine colour is the most practical indicator: pale yellow (like lemonade) means well-hydrated; dark yellow or amber means drink more; nearly clear means you may be over-hydrated. Thirst is also a reliable signal in healthy adults — if you feel thirsty, drink. Athletes and elderly adults should not rely on thirst alone, as these signals can be blunted.
Do I need to drink more water when exercising?
Yes. Exercise increases fluid losses through sweat. A general guideline: drink 400–600 ml of water 2 hours before exercise, 150–250 ml every 15–20 minutes during exercise, and 500–700 ml for every 0.5 kg of body weight lost during exercise. For sessions under 60 minutes at moderate intensity, water is sufficient — sports drinks are only necessary for prolonged (60+ min) intense exercise.