Water Intake Calculator

The water calculator determines your daily fluid needs based on your weight and activity level. An adult needs about 30 milliliters of water per kilogram of body weight – this is the baseline, while workouts, heat and dry climate add to it. Enter your weight and activity – the calculator shows your norm in liters and in 250-milliliter glasses.

How the water norm is calculated

The base formula: weight in kilograms × 30 milliliters. For a 70 kg person this is 2.1 liters a day. Recommendations from different institutes range from 30 to 35 milliliters per kilogram, and the popular "about 8 glasses" rule matches a 65–70 kg person. Importantly, this is all fluids from all sources – water, tea, coffee, soups, and the water in fruit and vegetables (up to 20% of the norm).

How to use the calculator

Enter your weight and honestly pick your activity level. Low – sedentary work without regular workouts. Moderate – exercising 1–3 times a week. High – almost daily workouts or physical work; at this level the calculator adds 800 milliliters to your norm. You will see the total in liters, its split into the base part and the activity add-on, plus the equivalent in 250 ml glasses – a handy way to track your day.

When you need more water

Needs rise in heat and low humidity, during and after workouts (an hour of activity loses 500–1000 milliliters through sweat and breathing), during pregnancy and breastfeeding, and with fever, vomiting or diarrhea. Heated indoor air is dry in winter, so needs are above average too. If you sweat – drink small amounts before, during and after the effort.

How not to under- or over-drink

The best guide is thirst: in a healthy person it signals the need accurately. Urine color is a simple hydration indicator: light yellow means you are fine, dark means you need more. Do not force water "past the point of no want": excess water flushes out electrolytes and is harmful with heart or kidney disease. Spread your norm evenly – large volumes at once absorb worse.

This calculation is for information only and is not medical advice. For heart, kidney conditions or edema, your water intake should be set by a doctor.

Frequently asked questions

How much water should I drink a day?
On average 30 ml per kilogram of weight: at 70 kg this is about 2.1 liters a day. With workouts, heat or a dry climate the norm rises by 0.4–1 liter. All fluids count – including tea, soups and the moisture in fruit.
Do tea and coffee count toward my water intake?
Yes. The water in them is absorbed the same way, and the mild diuretic effect of coffee is offset by moderate consumption. About 20% of the daily norm comes from food – soups, fruit and vegetables.
How do I know I drink too little water?
Simple signs: dry mouth, dark urine and infrequent urination, headache, weakness and poor concentration. Light yellow urine is a good indicator that you are getting enough.
Can I drink too much water?
Yes, excess water is dangerous – it dilutes the blood and flushes out electrolytes (hyponatremia). Do not force yourself to drink "when you do not want to" and do not exceed your norm by more than double. With heart or kidney disease, fluid intake must be set by a doctor.
Should I drink water during a workout?
Yes: an hour of activity loses 0.5–1 liter of sweat. Drink small amounts before, during and after training – roughly 150–250 ml every 15–20 minutes. Intense sessions longer than an hour also call for replacing salts.
Does water help with weight loss?
Water does not burn fat directly, but a glass of water before a meal moderately reduces appetite, and replacing sugary drinks with water cuts 200–400 "empty" calories a day. Sometimes thirst disguises itself as hunger – try a glass of water first.

Updated: Oct 14, 2026

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