Water Intake Calculator: How Much Water Should You Drink a Day?
Your details
General guidance for healthy adults, not medical advice. With kidney, heart or liver disease, diuretics, pregnancy or breastfeeding, or a fluid limit from your doctor, follow your clinician’s target. HydroBloom is not a medical device.
Your daily water goal
2,700ml
91.3 fl oz · 2.7 L
≈ 11 glasses of 250 ml
≈ 5 bottles of 500 ml
Enter your weight to see your goal.
How this number is worked out
- 154 lb (69.9 kg) × 35 ml
- 2,445 ml
- Activity · Moderate
- +250 ml
- Climate · Temperate
- +0 ml
- Total
- 2,695 ml
- Rounded to the nearest 50 ml
- 2,700 ml
Weights below 30 kg or above 250 kg are counted as 30 or 250 kg.
Enter your weight, how active you are and the climate you live in. You get a daily drinking goal in millilitres and fluid ounces — the exact number HydroBloom sets when you give it the same three answers.
How the water intake calculator works
The calculator follows the same four steps as the HydroBloom app. Nothing you enter is sent anywhere — the maths runs in your browser.
- Start from your body weight. Multiply your weight in kilograms by 35 ml (in pounds, that is about 0.54 fl oz per lb).
- Add for activity. Add nothing for low activity, 250 ml for moderate activity and 500 ml for high activity.
- Add for heat. Add 250 ml if you live in a hot or humid climate.
- Round and keep it realistic. Round to the nearest 50 ml and keep the result between 1,500 and 4,000 ml, so the goal stays a realistic daily habit.
Worked example: a 70 kg (154 lb) adult with moderate activity in a temperate climate. 70 × 35 = 2,450 ml, plus 250 ml for activity = 2,700 ml a day — about 91 fl oz, or 11 glasses of 250 ml.
How your number compares with official guidance
U.S. National Academies (NASEM)
About 3.7 litres of total water a day for men and 2.7 litres for women, counting all drinks and the water in food. Roughly 80% of it comes from drinks, including caffeinated ones, and 20% from food.
European Food Safety Authority (EFSA)
2.5 litres of total water a day for men and 2.0 litres for women, from drinks and food, assuming a moderate climate and moderate activity.
NHS (UK)
6 to 8 cups or glasses of fluid a day. Water, lower-fat milk, sugar-free drinks, tea and coffee all count.
Pregnancy and breastfeeding (EFSA)
About 300 ml a day more during pregnancy and about 700 ml more while breastfeeding. The calculator does not add this for you.
These are population reference values for total water, not personal targets. The calculator gives a personal goal for what you drink, scaled to your body, activity and climate. It is deliberately generous: falling a little short on a cool, quiet day is nothing to worry about, and healthy adults can also go by thirst. A goal simply helps if you tend to forget.
Why weight, activity and climate?
The largest study of how much water people actually turn over each day — Yamada et al. in Science (2022), which tracked water turnover in 5,604 people from 23 countries using isotope methods — found it was significantly associated with body size, physical activity and environmental conditions such as air temperature and humidity, as well as with age, body composition and pregnancy. This calculator asks about the first three. That is why the result is a starting point you can adjust, not a prescription.
Why this number — further reading
Water intake: common questions
How much water should I drink a day?
It depends on your size, activity and climate. A practical starting point is 35 ml per kilogram of body weight, plus 250–500 ml if you are active and 250 ml in hot weather. For a 70 kg adult with moderate activity that is about 2.7 litres (91 fl oz) of drinks a day. Official reference values for total water, including food, are 2.0–2.5 litres (EFSA) and 2.7–3.7 litres (NASEM).
How do I calculate my water intake by body weight?
Multiply your weight in kilograms by 35 ml, or your weight in pounds by about 0.54 fl oz. Add 250 ml for moderate or 500 ml for high activity, and 250 ml if the climate is hot. Round to the nearest 50 ml. The calculator above does all of this and shows its working.
Do coffee and tea count toward my water intake?
Yes. The U.S. National Academies count caffeinated drinks toward daily water intake, and the NHS lists tea and coffee among the drinks that count. Plain water is still the simplest choice.
Can you drink too much water?
Yes, although it is rare in healthy adults. Drinking a very large amount in a short time can dilute the sodium in your blood (hyponatraemia). That is one reason this calculator never goes above 4 litres, and why it is better to spread drinks across the day.
Should I drink more if I am pregnant or breastfeeding?
Usually a little, yes. EFSA suggests about 300 ml a day more during pregnancy and about 700 ml more while breastfeeding. The calculator does not add this automatically, so check the figure with your midwife or doctor.
Is this the same goal the HydroBloom app sets?
Yes. The calculator runs the same formula as the app: 35 ml per kilogram, the same additions for activity and climate, the same rounding and the same 1.5–4 litre range. Enter the same answers in the app and you get the same number.
Sources
- Report Sets Dietary Intake Levels for Water, Salt, and Potassium To Maintain Health and Reduce Chronic Disease Risk — U.S. National Academies (NASEM)
- EFSA sets European dietary reference values for nutrient intakes — EFSA
- Dietary Reference Values for nutrients — Summary report — EFSA
- Water, drinks and hydration — NHS
- Yamada Y, et al. Variation in human water turnover associated with environmental and lifestyle factors. Science 2022;378(6622):909–915 — Science
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