💧 Water Intake Calculator

How the Water Intake Calculator Works

This calculator gives a general estimate of daily drinking water (plain water and other beverages) for a healthy adult. It starts from a common body-weight guideline of about 30–35 ml per kilogram, then adds extra for exercise, hot weather, pregnancy, or breastfeeding.

For context, reference values for total water intake from all sources (drinks and food) are about 3.7 litres a day for men and 2.7 litres for women according to the US National Academies, and about 2.5 and 2.0 litres according to the European Food Safety Authority. Roughly 20% of that usually comes from food. Needs vary a lot from person to person, and thirst and pale-yellow urine are practical everyday guides. People with kidney, heart, or liver conditions, or who have been told to limit fluids, should follow their doctor's advice instead of this estimate.

Formula

Base (drinks)  = body weight (kg) × 30–35 ml
Exercise       + about 0.6 L per hour of activity (range 0.4–0.8 L/h)
Hot climate    + about 0.5 L
Pregnancy      + about 0.3 L      Breastfeeding  + about 0.7 L

Exercise, pregnancy, and breastfeeding additions follow commonly cited guidance (e.g. American College of Sports Medicine ranges and EFSA reference values).

How to Use It

1. Enter your weight and choose kg or lb.
2. Enter your average daily exercise in minutes.
3. Tick any extra factors that apply.
4. Read your estimated daily drinking range in litres, glasses, and US ounces.

Frequently Asked Questions

How much water should I drink a day?

A common guideline for healthy adults is about 30–35 ml of fluid per kilogram of body weight, plus extra for exercise and heat. For a 70 kg adult that is roughly 2.1–2.5 litres of drinks per day, but individual needs vary.

Does coffee or tea count toward water intake?

Yes. All beverages contribute to your fluid intake, including tea and coffee in moderate amounts, and water-rich foods such as fruit, vegetables, and soup add more.

Can you drink too much water?

Yes. Drinking very large amounts in a short time can dilute blood sodium (hyponatremia), which can be dangerous. It is a particular risk during long endurance events. Spread intake through the day and drink according to thirst.

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Formula and content last reviewed: September 2026. All calculations run in your browser — nothing you enter is sent to or stored on our servers.