Optimal drinking regime: how much water to drink according to weight and age (calculator)

Optimal drinking regime: how much water to drink according to weight and age (calculator)

How much water should we drink? There are many answers to this question today. You can find more than enough of them on the internet. But what is the realistic amount of water that our body needs? What is a healthy drinking regime? An optimal drinking regime can be recommended, but it is always individual. The calculator is only for guidance. In practice, dehydration is very common. People are mistakenly convinced that they drink enough fluids.
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Drinking plan - calculator: how much water should we drink per day?

What is drinking and what is its importance?

Drinking is the supply of water to a person's body. It must cover the body's daily needs and its water losses.

Water is necessary for the human body. It cannot produce it by itself. Approximately 60-70% of the body is made up of water.

When we drink too little fluid = we are tired, weak, literally emaciated.
Dehydrated. A common cause of headaches.

Too much water is not good for the body either.

We must take into account individual needs, overall physical or mental stress, a person's illness and many other factors. Last but not least, environmental conditions.

And also age.

Sometimes we need less and sometimes more water.

Once the temperature outside rises above 30 °C, we need more water. At high temperatures, we lose water through breathing and sweating.

The amount of fluid our bodies excrete each day:

  • 800-1400 ml approximately we urinate
  • 600-800 ml of water is expelled by breathing as steam
  • 500 ml leave through perspiration
  • about 100 ml are excreted in faeces
  • total = 2000 to 2800 ml

The values rise sharply with high physical exertion and during hot summer days. Then the water loss should be estimated at 3 to 5 times.

The increase in loss should be compensated by increased intake.


It is said that we should drink about 1.5-2 litres of water per day.

How can I calculate my approximate daily water requirement?

The basic calculation is based on age per kilogram of body weight.

  • The conversion assumes ideal conditions:
    • ambient temperature of 22 °C
    • relative humidity of around 60%
    • without exertion and with little perspiration

Drinking regime according to weight and age in the table (also for children)

The brief summary shows the values under ideal conditions.

How much water should I drink? The table shows the amount by age per 1 kg of body weight

Age Approximate amount of fluid per day per 1 kg body weight (ml/kg body weight)
Premature newborn (1st day of life) 50-70 ml
Preterm newborn (2nd day of life) 70-90 ml
Preterm newborn (3rd day of life) 80-100 ml
Premature newborn (4th day of life) 100-120 ml
Premature newborn and infant (10th day of life to 7th month) 150-160 ml
Infant (8th day to 12th month) 100-140 ml water
2nd year 80-120 ml of water
Child from 3 to 5 years 80-100 ml of water
Child from 6th to 10th year 60-80 ml of water
Child from 11 to 14 years 50-70 ml of water
Children and adolescents from 14 to 18 years 40-60 ml of water
Adult 20-45 ml of water

An adult weighing 70 kg should drink 1400 ml (1.4 litres) to 3150 ml (3.15 litres) of fluid. On average, this means 2-2.5 litres.

A 5-year-old child weighing 20 kg should drink about 1600 ml (1.6 litres) to 2000 ml (2.0 litres) in 24 hours.


  • You need to drink more often in smaller amounts, for example a glass of water every hour or 10 x 2.5 dcl of water. Everyone needs to set their own frequency and amount.
  • In the morning after waking up it is advisable to drink about 3 dcl of water.
  • The main meal should not be washed down with too much water.
  • Pouring water from a bottle can improve the overview.
  • Drinking water or non-carbonated spring water is considered a suitable liquid.
    • Inappropriate beverages include sweetened sodas, cola drinks, flavoured mineral and carbonated drinks, nectars and juices. Their intake should be limited.
      • Excessive intake is a risk factor for the development of obesity and other health complications. In addition, sugary drinks promote tooth decay.

Do not forget to increase the amount of fluids in heated and air-conditioned environments. Both situations dry out the air and the mucous membranes of the nose and mouth. The body needs a higher amount of fluids.

Am I not drinking enough?

How do I know if I've been drinking too little?

  • feeling thirsty.
  • fatigue, drowsiness, weakness
  • dark urine and urinating small amounts of urine
  • dry skin and lips, tongue
  • body tremors
  • pain and dizziness
  • low blood pressure, rapid pulse, collapse
  • coffee, tea and alcohol increase the amount of urine produced

Decreased mental performance, fatigue, drowsiness or headache are often the first signs of insufficient water intake.

The frequency of urination will decrease. You will produce less urine. Urine will be dark yellow and may smell more.

Adequate amounts of water will give you good physical and mental vitality. It will improve your mood, emotions, performance, and overall well-being.

Water poisoning: Is it possible to drink too much fluid?


It is possible to put too much fluid into the body.

How much is too much?

You can't drink 5 litres of water at rest and without activity. You would have to have a good reason for doing so.

10 litres a day can put a significant strain on the heart and kidneys.

You can get water poisoning in a very short time. It is also possible to get water poisoning if you exceed reasonable limits for a long time.

Our body tries to be sensible with all substances and minerals. When drinking excessive litres of water over a long period of time, mineral levels are disturbed. This can have fatal consequences.

What causes excessive drinking of water?

Sodium deficiency (hyponatremia) is dangerous when the blood sodium level is below 130 mmol/l.

Water intoxication can manifest as headache, fatigue, nausea vomiting, muscle cramps or disorientation.

Do not put your health and life at risk.

Last words in conclusion

Contradictory information can be found in various publications.

Some experts do not include food (such as milk, soup, tea and coffee) in the total daily intake.

Some include these items as well. According to them, food covers about 20% of the value of our fluid intake (fruit, vegetables, milk).

Similarly, the most commonly quoted value is 2 litres.

According to some sources, an intake of 2 litres per day is not supported by sufficient scientific evidence.

Who is to know? What value should I remember?

6-8 glasses should be a sufficient limit in one day.

  • if a glass is 2.5 dcl = 1.5 to 2 litres
  • if the glass is 3 dcl = 1.8 to 2.4 litres
  • approximately 2 litres for a man and 1.6 litres for a woman in one day
  • the amount increases depending on daily activities


Other publications advise that men should drink approximately 15.5 glasses (about 3.6 litres) per day and women 11.5 glasses (about 2.6 litres) per day.


When drinking enough, we rarely feel thirsty. Urine is light yellow or colourless.

If we are not drinking enough, we urinate little and the urine is dark. We feel thirsty and less vital.


Pay attention to the peculiarities of each of us.

If a person is being treated for heart failure, for example, or has non-functioning kidneys, these calculations are invalid. The amount of fluids per day should be consulted with a doctor.

For more on drinking (and related employer obligations) and dehydration, see the articles:

Important notice:

Please remember that the results of our health calculators and analyzers are for guidance purposes only. They are not a substitute for a professional examination or the advice of a doctor, pharmacist or other health care professional.

Each person is unique, and everyone's needs may vary. Calculators and analyzers have limitations and do not provide a comprehensive individual view of health.

Their use is at your own risk. Neither the site operator nor the author is responsible for misuse and misinterpretation of information obtained through their use. By using the calculators and analyzers, you agree to these terms and conditions and neither the operator nor the author shall be liable for any consequences.

You are advised to consult a professional for your medical condition. Remember that health is an important topic and any decisions should be made in consultation with a professional.

This calculator/analyzer is not a medical tool or medical aid. Consult your doctor about your health problem.

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