Water Intake Calculator
See roughly how much water your body needs each day. The estimate starts from your weight, then adjusts for how much you exercise and the climate you live in.
Enter your weight and press Calculate to see your daily water target.
How the estimate is built
Start from weight
The base target uses about 35 millilitres of water per kilogram of body weight, a common guideline for healthy adults.
Add for exercise
Roughly 350 millilitres are added for every half hour of activity to replace what you lose through sweat and breathing.
Adjust for climate
Hot or humid conditions raise the total further, since heat drives up fluid loss even when you are not exercising.
Why hydration matters
It runs your body
Water regulates temperature, cushions joints, carries nutrients and clears waste. Even mild dehydration can dent concentration, mood and physical performance.
Food counts too
About a fifth of your fluid usually comes from food, especially fruit, vegetables and soups. The rest is what you actually drink through the day.
Private by design
Your weight and activity stay in your browser. Nothing is uploaded or stored, so you can check your target as often as you like.
How much water do you really need?
The old advice to drink eight glasses a day is easy to remember but ignores the fact that a 55 kilogram office worker and a 95 kilogram athlete have very different needs. Tying the target to body weight and activity gives a far more personal starting point.
The weight-based guideline
Many nutrition sources suggest around 30 to 40 millilitres of water per kilogram of body weight for healthy adults. This calculator uses 35 as a sensible midpoint, then layers activity and climate on top. The result is total fluid, and remember that food typically provides a further 20 percent or so.
Signs you are well hydrated
The simplest check is the colour of your urine: pale straw suggests you are on track, while dark yellow is a nudge to drink more. Thirst, dry lips and low energy in the afternoon are other everyday clues that your intake has slipped.
| Body weight | Rough base target |
|---|---|
| 50 kg | ~1.8 litres |
| 70 kg | ~2.5 litres |
| 90 kg | ~3.2 litres |
When to drink more or less
Hot weather, intense exercise, fever, pregnancy and breastfeeding all raise your needs. On the other side, certain heart and kidney conditions call for fluid limits, so anyone with a medical reason to restrict water should follow their clinician rather than a general formula.
Can you drink too much?
Very rarely, drinking huge volumes in a short time can dilute blood sodium to dangerous levels. For almost everyone this is not a concern, but it is a reason to spread your intake across the day rather than forcing litres at once.
Frequently asked questions
How is the target calculated?
It starts at about 35 millilitres per kilogram of body weight, adds roughly 350 millilitres per 30 minutes of exercise, and increases the total in warm or hot climates.
Does tea and coffee count?
Yes. Despite their reputation, moderate caffeinated drinks still contribute to your daily fluid. Water is simply the cheapest and most reliable option.
Is the number just water or all fluids?
It is total fluid intake. Since food provides around a fifth of that, the amount you need to actually drink is usually a little less than the figure shown.
Are my details saved?
No. The calculation happens in your browser and nothing you enter is uploaded or stored anywhere.
Should I drink more when exercising?
Yes. Add fluid before, during and after activity. The calculator already increases your target based on the minutes you enter.
Can I drink too much water?
For most people it is very hard to overdo it. Only extreme intake over a short period is risky, so spread your drinking across the day.