Water Intake Calculator
Enter your weight, age, exercise time and climate. The calculator converts your personal hydration target into litres, fluid ounces, 250 ml cups and standard water bottles, and then splits it into an hour-by-hour drinking schedule you can actually follow.
How Much Water Should You Drink Per Day?
There is no single number that fits everyone. The most widely used clinical starting point is 30 to 40 ml of fluid per kilogram of body weight per day for healthy adults, which works out to roughly 0.5 to 0.6 US fluid ounces per pound. On top of that baseline you add fluid for anything that makes you lose water faster: exercise, heat, altitude, fever, pregnancy and breastfeeding.
For reference, the U.S. National Academies suggest a total daily fluid intake of about 3.7 litres (125 oz) for men and 2.7 litres (91 oz) for women, including water from food and all beverages. Because roughly 20% of that arrives through food, the amount you actually drink is usually closer to 3.0 L and 2.2 L respectively.
The formula this calculator uses
Daily water (ml) = weight in kg × ml-per-kg × climate factor + 350 ml per 30 min of exercise + pregnancy or breastfeeding allowance
- ml per kg: 40 ml for teens (14–17), 35 ml for adults (18–55), 30 ml for seniors (56+). Older adults have a weaker thirst signal and lower kidney concentrating ability, so the target is lower but the risk of under-drinking is higher.
- Climate factor: 1.0 cool, 1.1 warm or humid, 1.2 hot or tropical.
- Exercise: about 350 ml (12 oz) per 30 minutes of moderate activity — more if you sweat heavily.
- Pregnancy: +300 ml per day. Breastfeeding: +700 ml per day.
Daily Water Intake Chart by Body Weight
Baseline figures for a moderately active adult in a temperate climate (35 ml/kg, no exercise adjustment). Add roughly 350 ml for each 30 minutes of training.
| Body weight | Litres/day | US fl oz/day | Cups (250 ml) | 500 ml bottles |
|---|---|---|---|---|
| 45 kg (99 lbs) | 1.6 L | 53 oz | 6.3 | 3.2 |
| 55 kg (121 lbs) | 1.9 L | 65 oz | 7.7 | 3.9 |
| 65 kg (143 lbs) | 2.3 L | 77 oz | 9.1 | 4.6 |
| 70 kg (154 lbs) | 2.5 L | 83 oz | 9.8 | 4.9 |
| 80 kg (176 lbs) | 2.8 L | 95 oz | 11.2 | 5.6 |
| 90 kg (198 lbs) | 3.2 L | 107 oz | 12.6 | 6.3 |
| 100 kg (220 lbs) | 3.5 L | 118 oz | 14.0 | 7.0 |
| 110 kg (243 lbs) | 3.9 L | 130 oz | 15.4 | 7.7 |
Worked Example
A 78 kg man who trains for 60 minutes a day in a hot climate:
- Base: 78 kg × 35 ml = 2,730 ml
- Climate (hot, ×1.2): 2,730 × 0.2 = +546 ml
- Exercise: 60 min ÷ 30 × 350 ml = +700 ml
- Total: 2,730 + 546 + 700 = 3,976 ml ≈ 4.0 L (134 oz)
Since about 20% of fluid comes from food, he would aim to actually drink around 3.2 L and let meals cover the rest.
How Much Water to Drink to Lose Weight
Water does not burn fat directly, but it helps in three measurable ways: it fills stomach volume before meals, it replaces liquid calories, and mild dehydration is often misread as hunger. A common evidence-backed pattern is 500 ml (17 oz) of water 30 minutes before each main meal, which in trials has been linked to a modest extra weight loss over 12 weeks. Keep your total intake at the calculated target and take those 500 ml out of it rather than adding on top.
Signs You Are Not Drinking Enough
- Urine colour — pale straw is the target. Dark yellow or amber means drink now. This is the single most practical daily check.
- Fewer than 4 bathroom trips a day for an average adult.
- Afternoon headaches, dizziness on standing, or brain fog — losing just 1–2% of body water measurably reduces concentration.
- Dry mouth, cracked lips, poor skin turgor (pinched skin on the back of the hand is slow to flatten).
- Muscle cramps during training, especially in the heat.
Can You Drink Too Much Water?
Yes. Drinking far beyond your needs — typically more than about 1 litre per hour sustained — can dilute blood sodium and cause hyponatraemia, which is dangerous and occasionally fatal. It is rare in daily life and mostly seen in endurance athletes and in water-drinking challenges. Spread your intake across the day instead of drinking large volumes at once, and if you sweat for more than 90 minutes, include electrolytes rather than plain water alone. People with kidney disease, heart failure or on diuretics should follow their doctor's fluid limits instead of a general calculator.
Do Coffee, Tea and Food Count?
Yes. Every fluid contributes: water, milk, juice, tea and coffee all count toward your total. Caffeine is a mild diuretic, but at normal intakes (up to about 400 mg, roughly four cups of coffee) the net effect is still positive hydration. Water-rich foods matter too — cucumber, watermelon, tomatoes, oranges, soups and yoghurt are 80–95% water and typically supply about a fifth of your daily fluid. Alcohol is the exception: it suppresses vasopressin and increases fluid loss, so alcoholic drinks should not be counted toward your target.
Frequently Asked Questions
How much water should I drink a day for my weight?
Multiply your weight in kilograms by 35 ml (adults 18 to 55). A 70 kg adult needs about 2.45 litres, or 83 US fluid ounces. In pounds, multiply by about 0.5 to get fluid ounces. Add roughly 350 ml for every 30 minutes of exercise and 10 to 20 percent more in hot weather.
Is 8 glasses of water a day enough?
Eight 8-ounce glasses is about 1.9 litres, which is a reasonable minimum for a small, sedentary adult in a cool climate but too low for most people who are over about 55 kg, exercise, or live somewhere hot. The rule has no strong research behind it. A weight-based target is more accurate.
How much water should I drink to lose weight?
Use the same weight-based target and time it around meals: about 500 ml of water 30 minutes before each main meal helps reduce calorie intake. Replacing sugary drinks with water is the bigger win. Water alone does not burn fat, but it supports a calorie deficit.
Does coffee and tea count toward daily water intake?
Yes. Coffee and tea are net hydrating at normal intakes, despite caffeine being a mild diuretic. All beverages count toward your total fluid. Alcohol is the exception because it increases fluid loss and should not be counted.
How do I know if I am drinking enough water?
Check your urine colour. Pale straw yellow means you are well hydrated; dark yellow or amber means drink more right away. Other signs of good hydration are urinating at least four to six times a day and not feeling thirsty, headachy or foggy in the afternoon.
Can drinking too much water be harmful?
Yes. Sustained intake above roughly one litre per hour can dilute blood sodium and cause hyponatraemia, which can be serious. Spread your intake through the day, add electrolytes for sessions longer than 90 minutes, and follow medical advice if you have kidney or heart conditions.