Hydration Calculator

Estimate your daily water needs based on your profile, physical activity, and environment.

How this calculator works

The calculator first estimates a base water need from your weight, following a logic similar to that used to estimate water needs based on body mass. This baseline is then adjusted for sex, and increased based on your physical activity level and climate conditions (heat, humidity, altitude, heating), all of which increase water loss through sweat and breathing. For pregnant or breastfeeding women, an extra amount is added in line with common nutritional guidelines. The total is then split between water to drink (about 80%) and water naturally provided by food (about 20%).

The calculation logic

Base need ≈ 100 ml/kg for the first 10 kg + 50 ml/kg for the next 10 kg + 20 ml/kg beyond that, then adjusted by sex. Physical activity (+350 to +750 ml), climate (+500 to +750 ml), and, where relevant, pregnancy (+300 ml) or breastfeeding (+700 ml) are then added on top.

Frequently asked questions

Is this calculator valid for everyone?

It provides a general estimate for a healthy adult. It does not replace medical advice, especially for people with kidney or heart conditions, those on specific medication, or children.

Why does climate affect my water needs?

Heat, humidity, altitude, and indoor heating all increase sweating and water loss through breathing, which increases the amount needed to compensate.

Do coffee and alcohol count toward my water intake?

Coffee and tea generally contribute to hydration despite their mild diuretic effect. Alcohol, on the other hand, promotes dehydration and should not be counted as fluid intake.

Should I only drink when I feel thirsty?

Thirst isn't always a reliable signal, especially for older adults or during intense physical effort. It's better to spread your fluid intake evenly throughout the day.

How can I recognize signs of mild dehydration?

Dark urine, a dry mouth, fatigue, or headaches are common signs that can indicate insufficient water intake.

Are these figures a medical prescription?

No, this is an informative estimate based on general nutritional guidelines, not personalized medical advice. Consult a healthcare professional for specific situations, such as a high-risk pregnancy or a chronic condition.

Other tools that pair well with this one.

Health