Water Intake Calculator
Estimate your daily water intake based on body weight and activity level.
TL;DR — Water Intake Calculator: A water intake calculator estimates how much water you should drink per day to stay hydrated. The common rule is about 30–35 ml per kilogram of body weight per day, increased for hot weather and exercise. Beverages and water-rich foods all count toward total fluid intake.
What is the Water Intake Calculator?
A water intake calculator estimates how much water you should drink per day to stay hydrated. The common rule is about 30–35 ml per kilogram of body weight per day, increased for hot weather and exercise. Beverages and water-rich foods all count toward total fluid intake.
How to use the Water Intake Calculator
- Choose units (kg or lb).
- Enter your body weight.
- Select an activity level — sedentary, light, moderate or active.
- Read your recommended daily water intake in litres and US cups.
Formula
Base water (ml/day) = weight(kg) × 33 Adjusted = Base × Activity Factor
Activity factors: sedentary 1.0 · light 1.1 · moderate 1.2 · active 1.4. Hot climates add another 10–20%.
Worked example
A 70 kg moderately active adult: 70 × 33 = 2,310 ml base, × 1.2 activity = 2,772 ml ≈ 11.7 US cups per day.
Frequently asked questions
Is "8 glasses a day" the right amount?
It is a rough guideline. Actual needs depend on body size, activity, climate and diet. The 33 ml/kg formula gives a more personalised target.
Do other drinks count?
Yes. Tea, coffee, milk, juice and water-rich foods (fruit, vegetables, soup) all contribute to hydration.
What are signs of dehydration?
Dark yellow urine, thirst, dry mouth, headache, fatigue and dizziness. Pale yellow urine is the simplest hydration indicator.
Can you drink too much water?
Yes — extreme over-hydration (hyponatraemia) can be dangerous. Stick within reasonable daily targets and listen to thirst.
Should I increase intake for exercise?
Yes. Add about 500–700 ml for every hour of moderate exercise, more in heat.