Water Intake Calculator
Your daily drinks goal in litres, cups and bottles, from weight, activity and heat.
Updated October 2026
General guidance for healthy adults. Needs vary with health, medicines, climate and pregnancy. Follow your clinician's advice if you have a heart, kidney or other condition.
Your daily water goal
Example for 70 kg, moderate activity, age 30.
How the number is built
Compare with EFSA reference values
EFSA's adequate intake of total water is 2.0 L a day for adult women and 2.5 L for men, and about 20% of it usually comes from food. That leaves about 1.6 L and 2.0 L to drink.
Tea, coffee and milk count towards this drinks goal. The water in food comes on top (about a fifth of total water), so it is not included.
Pregnant or breastfeeding? Needs are higher (EFSA's reference is 2.3 L of total water in pregnancy and 2.7 L while breastfeeding), so use your midwife's or doctor's advice instead of this number.
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Read the full disclaimer
Every number on this page (calorie targets, macro splits and any suggested meal plan) is produced by formulas (Mifflin-St Jeor for basal metabolic rate, standard activity multipliers) or, for AI-generated meal plans, by a language model applying those same formulas. On meal-plan pages the carbohydrate figure for each meal is calculated by difference: total calories minus protein and fat calories, divided by 4. It is not measured or estimated on its own, so read it as an arithmetic balance and not as an independent nutritional analysis of the dish. None of it is individualized medical or nutritional advice, and none of it has been reviewed by a registered dietitian, physician or other licensed healthcare professional.
Ask your doctor or a registered dietitian what is right for you before starting a new diet, especially if you are pregnant or breastfeeding, have a diagnosed medical condition, take prescription medication, or have a history of disordered eating. If you have kidney disease or another medical condition, ask your clinician before raising protein.
Mealyno never recommends a calorie target below your calculated Basal Metabolic Rate (BMR), the minimum energy your body needs at complete rest. Even the most aggressive weight-loss setting is clamped at that floor.
Calorie and BMR estimates use the Mifflin-St Jeor equation (Mifflin MD, St Jeor ST, et al. Am J Clin Nutr. 1990).
Generated: October 2026
Most advice about water is one number for everyone, usually eight glasses. Body size, how much you move and how hot it is all change what you need, so this calculator starts from your body weight instead. It multiplies your weight by 30 to 35 ml per kilogram depending on how active you are, adds 500 ml when it is hot, and rounds to the nearest 50 ml. The result is a daily drinks goal for a healthy adult, shown in litres, 250 ml cups, 500 ml bottles and US fluid ounces.
The weight-based rule is a practical rule of thumb, not a law of physiology. For a reference point from outside this page, the European Food Safety Authority's 2010 opinion on dietary reference values for water sets an adequate intake of total water at 2.0 litres a day for adult women and 2.5 litres for adult men. Total water means all drinks plus the water in food, which usually supplies about a fifth. The calculator shows how your goal compares with those figures, so you can see whether the number sits in a sensible region.
Two limits keep the result sensible. The goal is held between 1.5 and 4 litres, because a formula applied to a very light or very heavy person can drift outside what anyone should plan for without personal advice. And it is for adults: children and teenagers have their own reference values, so under-18s get no number. If you are pregnant or breastfeeding, the reference intakes are higher (EFSA lists 2.3 and 2.7 litres of total water), and your midwife or doctor is the right guide.
What counts? Water, sparkling water, tea, coffee, milk and the water in soup, fruit and vegetables all count towards your total. Sugary drinks count as fluid but come with sugar, so the Mealyno app logs them on a separate line. For most people plain water is the easy default, and thirst, the colour of your urine and how you feel are the day-to-day checks. People with heart, kidney or liver conditions, or who take medicines that affect fluid balance, are often given a personal limit by their clinician, and that limit replaces any calculator.
Use the result as a starting point and adjust over a week. Share the link or download the card to send it to a training partner or a client, or embed the calculator on your own site with the snippet further down this page.
How the calculation works
- Base = body weight (kg) x ml per kg by activity: sedentary 30, light 31, moderate 33, active 34, very active 35.
- Add 500 ml if it is hot where you live, work or train. The sum is held between 1,500 and 4,000 ml and rounded to the nearest 50 ml.
- Compare with EFSA's 2010 adequate intake of total water: 2.0 L for women, 2.5 L for men, about 20% of it from food. The result is a general reference for healthy adults, not a prescription.
Water intake worked example
Take an adult who weighs 70 kg and does moderate exercise. 70 x 33 = 2,310 ml, which rounds to the nearest 50 ml as 2,300 ml: 2.3 litres, 9 cups of 250 ml or 4.5 bottles of 500 ml. Spread over 16 waking hours that is about 140 ml an hour.
On a hot day the same person adds 500 ml and the goal becomes 2,800 ml, or 2.8 litres. A 55 kg person who sits most of the day gets 55 x 30 = 1,650 ml. A 120 kg, very active person in the heat adds up to 4,700 ml and is held at 4,000 ml, a reminder that the calculator does not replace a coach or clinician for endurance sport.
Compare with the EFSA reference values: 2.0 litres of total water for women and 2.5 litres for men, of which about a fifth normally comes from food, leaving roughly 1.6 and 2.0 litres to drink. The 70 kg example sits a little above both, which is expected, because the weight rule scales with body size and activity while EFSA gives one value per sex.
What to do with this number
Spread the goal across the day instead of drinking it in a few large doses. A glass with each meal and one between meals gets most people most of the way, and the per-hour line shows what an even pace looks like.
Treat the goal as the target for drinks, then let thirst, urine colour and how you feel guide small changes. Add more on hot days, during long training sessions and when you are unwell with a fever, and follow your clinician if you have been given a fluid limit.
Water sits next to the other numbers that shape a day of eating. The calorie calculator turns your energy needs into a target, and the protein calculator shows a range in grams. Mealyno logs your water next to your meals if you want one place for both.
Water intake questions
How much water should I drink a day?
For a healthy adult, the calculator multiplies body weight by 30 to 35 ml per kilogram depending on activity, adds 500 ml in hot weather, and holds the result between 1.5 and 4 litres. EFSA's reference for total water, including food, is 2.0 litres for adult women and 2.5 litres for adult men.
Is eight glasses a day a real rule?
It is a round number that is easy to remember, not a measured requirement. Eight 250 ml glasses is 2 litres, which happens to be close to EFSA's figure for women, but your size, activity and climate move the right number up or down.
Do coffee and tea count towards my water?
Yes. Tea, coffee, milk and the water in food all count towards total water. Plain water is the simplest default, and sugary drinks are worth tracking separately because they add sugar as well as fluid.
Do I need more water when I exercise or when it is hot?
Usually yes. The calculator raises the per-kilogram rate with activity and adds 500 ml for heat. Long sessions, heavy sweating and illness with a fever can need more than any formula gives, so listen to thirst and ask a coach or clinician for endurance sport.
Can I drink too much water?
Yes. Drinking very large amounts in a short time can be harmful, which is one reason the goal is capped at 4 litres and best spread over the day. If you have heart, kidney or liver disease, or take medicines that affect fluid balance, follow your clinician's limit instead of this number.
Does the water in food count?
Yes. About a fifth of total water intake normally comes from food, such as soup, fruit and vegetables. This calculator's goal is for drinks, so it sits below EFSA's total-water figures by roughly that share when the two are compared.
Is this calculator for children or pregnancy?
No. It is for healthy adults. Children and teenagers have their own reference values, so under-18s get no number. In pregnancy and while breastfeeding the reference intakes are higher, so follow your midwife or doctor.
Sources
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