Water Intake Calculator
One number is all it takes. See how much water to drink today — in cups and bottles.
Unit
This looks unusually high — double-check your input.
Your daily water target
Drinking this much in a short time can cause hyponatremia — consult a professional.
Includes the ~20% of water you get from food.
Estimating a daily water target (a starting point, not medical advice)
Most people have no reliable intuition for how much water a day is "enough," and the popular eight-glasses rule ignores that a 55 kg person and a 95 kg person have very different needs. This calculator gives a personalized estimate from your body weight and activity level so you have a concrete number to aim at. It is general wellness guidance for healthy adults, not a medical prescription — if you are pregnant, or you manage a kidney, heart, or liver condition, follow the fluid targets your clinician sets, which may be deliberately higher or lower than a generic formula.
How the estimate is built
The base target uses 33 mL of water per kilogram of body weight, the middle of the commonly cited 30–35 mL/kg range. Because roughly 20% of a typical person's water already comes from food — fruit, vegetables, soup — the figure here reflects that context rather than assuming you must drink every drop. On top of the base, an activity allowance is added: +0 mL for a mostly sedentary day, +350 mL for light-to-moderate exercise (1–3 times a week), and +700 mL for hard training or physical work (4+ times a week). The result is shown in liters, in ~240 mL cups, and in 500 mL bottles so it maps onto whatever you actually drink from.
Worked examples
Quick reference by weight (sedentary base, before activity)
| Body weight | Base target | ≈ Cups (240 mL) | ≈ Bottles (500 mL) |
|---|---|---|---|
| 50 kg | 1.65 L | 7 | 3.3 |
| 60 kg | 1.98 L | 8 | 4.0 |
| 70 kg | 2.31 L | 10 | 4.6 |
| 80 kg | 2.64 L | 11 | 5.3 |
| 90 kg | 2.97 L | 12 | 5.9 |
| 100 kg | 3.30 L | 14 | 6.6 |
Reading the result sensibly
- Coffee and tea count. Caffeine is only a mild diuretic at normal intakes, so ordinary cups of coffee and tea contribute to your fluids on balance — you do not need to "make up" for them.
- Thirst and urine colour are better real-time signals than hitting an exact number. Pale-straw urine usually means you are well hydrated; dark yellow suggests you need more.
- More is not always better. Drinking a very large volume in a short time can dilute blood sodium and cause hyponatremia, which is dangerous. A practical ceiling is about 1 liter in any single hour — spread intake across the day.
What this tool cannot know
The estimate does not account for climate, fever, breastfeeding, medications such as diuretics, altitude, or individual medical conditions, any of which can move your real requirement substantially. Treat the number as an informed default to build a habit around, and defer to a qualified professional for anything clinical. Your weight and activity choice stay in your browser and are never uploaded.
Sources & further reading
Frequently asked questions
How much water should I drink a day?
A common guideline is 30–35 mL of water per kilogram of body weight. This water intake calculator uses 33 mL/kg — the middle of that range — so a 70 kg adult gets about 2.3 liters (roughly 9–10 cups) before activity. Needs vary with climate, health and pregnancy, so treat the number as a starting point, not a strict rule.
Do coffee, tea and soup count toward water intake?
Yes, mostly. Coffee, tea, milk, juice and watery foods like soup, fruit and vegetables all add to your daily fluids. Caffeine has only a mild diuretic effect at normal amounts, so a regular cup of coffee still hydrates you on balance. This calculator already assumes about 20% of your water comes from food, so it targets what you actually drink.
Can drinking too much water be dangerous?
It can. Drinking very large volumes in a short time can dilute blood sodium and cause hyponatremia, which is dangerous. As a rule of thumb, avoid drinking more than about 1 liter in a single hour and spread your intake across the day. If your target here is very high, it reflects a large body weight or heavy activity — consult a professional before pushing far beyond it.
How much extra water do I need on workout days?
This water intake calculator adds a fixed activity allowance on top of the base amount: +0 mL for a mostly sedentary day, +350 mL for light-to-moderate exercise (1–3 times a week) and +700 mL for hard training or physical work (4+ times a week). On intense or hot days you may need more to replace sweat, so drink to thirst and check that your urine stays pale.
Is my weight sent to a server?
No. This water intake calculator runs entirely in your browser — your weight and activity level are never uploaded to any server. Your last entry is saved only in your browser's localStorage so the form is ready next time, and you can clear it anytime.