Daily Water Intake Calculator

Find out how much water you should drink each day based on your weight and activity level.

General wellness information only. Not medical advice. Consult a doctor if you have kidney or heart conditions.

Your weight

Activity level

Climate

Frequently Asked Questions

How is daily water intake calculated?

A common guideline is 35ml per kilogram of body weight, adjusted for activity level, climate, and individual factors. This tool uses that as a starting baseline.

Does coffee and tea count toward my water intake?

Moderate amounts of coffee and tea do contribute to hydration, though pure water is always the best source. High caffeine intake has a mild diuretic effect.

Should I drink more water if I exercise?

Yes. Physical activity increases water loss through sweat. The calculator accounts for this with the activity level selector.

Is this medical advice?

No. This is general wellness information only. People with kidney conditions, heart conditions, or other health issues should consult a doctor about their fluid intake.

What counts as a cup of water?

One standard cup is 250ml or approximately 8 fluid ounces.

How Much Water Should You Actually Drink?

The famous "eight glasses a day" recommendation has no strong scientific basis. It appears to originate from a 1945 U.S. Food and Nutrition Board guideline that recommended 2.5 litres of water daily — but included a sentence noting that most of this would come from food. The "8×8" simplification (eight 8oz glasses) dropped that context and spread widely.

What the research actually says

Current evidence-based recommendations are individualised by body weight and activity level. The European Food Safety Authority recommends 2 litres for adult women and 2.5 litres for adult men from all sources — food and drink combined. About 20% of daily water intake typically comes from food. The remaining 1.6–2 litres needs to come from drinks.

Body weight is the most consistent predictor of hydration needs. A commonly cited clinical guideline is 35ml per kilogram of body weight per day for a sedentary adult. A 70kg person would need approximately 2.45 litres. A 90kg person would need approximately 3.15 litres. Physical activity, hot weather, illness, and breastfeeding all increase requirements significantly.

Thirst as a guide

For healthy adults without kidney disease, thirst is a reasonably reliable hydration signal. The kidney's ability to concentrate urine means mild dehydration is corrected quickly once fluid is consumed. The idea that thirst means you are "already dehydrated" is a fitness industry myth not supported by physiology research. However, elderly people often have reduced thirst sensitivity, making deliberate fluid intake more important with age.

Signs of adequate hydration

Urine colour is the most practical hydration indicator. Pale yellow indicates adequate hydration. Dark yellow suggests mild dehydration. Clear urine often suggests over-hydration, which, while not dangerous in the short term, is unnecessary. Urine should be pale yellow for most of the day.