How the water intake calculator works
The calculator keeps two figures strictly apart that many hydration calculators mix up:
- Fluid intake from beverages: the DGE reference value for your age group, for example 1,410 ml for ages 25 to under 51. If you exercise, roughly 0.5 to 1 liter per hour is added as a rough orientation.
- Total water: body weight times 30 to 35 ml per kilogram (up to under 51 years about 35 ml/kg, from 51 years about 30 ml/kg). This figure covers beverages, the water in solid food and the metabolic water your body produces.
An example: at 35 years and 70 kg, your beverage reference value is 1,410 ml, so around 1.4 liters. Your total water comes to 70 times 35 = 2,450 ml, so about 2.5 liters. With a typical diet, roughly half of your total water comes from beverages, and a substantial part is in your food, from cucumbers to soups. This is exactly where many calculators on the web go wrong: they apply the ml-per-kg rule of thumb directly to fluid intake and therefore systematically output values that are too high. For context, the EFSA gives an adequate total water intake of 2.0 liters for women and 2.5 liters for men, in each case including the water in food and assuming moderate temperature and moderate activity.
DGE reference values: water intake by age
The DGE breaks down the reference values for water intake by age group. All figures in ml per day:
| Age group | Beverages | Solid food | Metabolic water | Total water | Total water per kg |
|---|---|---|---|---|---|
| 15 to under 19 years | 1,530 | 920 | 350 | 2,800 | 40 ml |
| 19 to under 25 years | 1,470 | 890 | 340 | 2,700 | 35 ml |
| 25 to under 51 years | 1,410 | 860 | 330 | 2,600 | 35 ml |
| 51 to under 65 years | 1,230 | 740 | 280 | 2,250 | 30 ml |
| 65 years and older | 1,310 | 680 | 260 | 2,250 | 30 ml |
As a rule of thumb for adults: drink around 1.5 liters per day from beverages, which together with your food adds up to a total water intake of about 2.5 liters. For people aged 65 and older, the DGE adds: at least 1.3 liters, better 1.5 liters from beverages, because the sense of thirst often fades with age.
Coffee, tea and more: what counts toward your fluid intake?
The claim that coffee dehydrates the body persists stubbornly but is considered debunked. In its practice guide, the DGE explicitly states that coffee and tea also count toward your fluid balance, and classifies up to four cups of coffee per day as unproblematic. A controlled study by Killer, Blannin and Jeukendrup (2014, PLOS ONE) found no differences in total body water and hydration markers with moderate coffee consumption compared to water. Because of its stimulating effect, coffee still does not make a good thirst quencher: water and unsweetened teas remain the first choice. To work out how much caffeine per day is okay for you, use the caffeine calculator. Alcoholic drinks technically count as fluid too, but for obvious reasons they are not a recommended way to cover your needs.
Drink more during exercise and in hot weather
During exercise you lose about 0.5 to 1 liter of sweat per hour depending on intensity and temperature, and at high intensity or in heat considerably more. The American College of Sports Medicine gives an intake of about 400 to 800 ml per hour for endurance exercise, individually adjusted for sweat rate and body size. The practical rule the DGE endorses: drink 100 to 200 ml every 15 to 20 minutes. For sessions up to about one hour, fluid is not strictly necessary if you start well hydrated. A simple self-test: weigh yourself before and after training, one kilogram less corresponds to about one liter of fluid. There is no official formula for heat; what is certain is that your needs rise with high temperatures, dry air, fever, vomiting or diarrhea. In those situations, use thirst and a urine color that is as light as possible as your guide. By the way, a high energy expenditure also increases your water needs. To see how many calories you need per day, use our calorie calculator.
Limits of the calculator and sensible next steps
This calculator is aimed at healthy adults, and more is not automatically better. Drinking very large amounts in a short time can dilute the sodium level in your blood (hyponatremia or water intoxication), with symptoms ranging from headaches and nausea to serious complications. Those most at risk are endurance athletes with very high intakes. With some medical conditions it can also be necessary to restrict fluid intake, for example with heart failure, certain kidney conditions or liver cirrhosis. The DGE calls consulting your treating doctor essential in these cases.
In everyday life, a simple routine helps: a glass of water with every meal, a filled bottle within sight and water-rich foods on your plate. You will find ideas in our healthy recipes and easy-to-understand background knowledge in the nutrition basics. If you want to put your weight into perspective, the BMI calculator can help. And if you want to change your diet as a whole, the coach directory helps you find qualified support near you or online.