Answer 4 quick questions and we'll give you a personalised daily water intake plus a simple morning, afternoon and evening drinking plan.
35ml/kg base formula
Activity adjusted
Climate adjusted
Coffee deduction
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First things first — which units do you prefer?
Pick whichever feels natural to you.
2 of 4
How much do you weigh?
Your weight is the biggest factor in how much water your body needs daily.
kg
3 of 4
How active are you?
Think about a typical week including work and exercise.
What’s the climate like where you live?
Heat and humidity increase how much you sweat and lose fluid.
4 of 4
How many coffees a day?
Caffeine has a mild diuretic effect — we’ll add a little extra water to compensate. Enter 0 if you don’t drink coffee.
cups
Your Results
Daily Water Intake
2.5
litres per day
approx. 8 glasses of 300ml each
Base (no activity)
2.1L
2.1L
Weight base
—
Climate add
—
Coffee adjust
Your Daily Drinking Plan
Split across morning, afternoon and evening
Note: This calculator provides a general estimate based on widely accepted hydration guidelines.
Individual needs vary based on health conditions, medications, and diet. Always consult your doctor for personalised medical advice.
How Much Water Should You Drink Per Day?
Most health authorities recommend drinking between 2 and 3.7 litres of water per day for adults. However, the right amount varies significantly based on your body weight, how active you are, the climate you live in, and other lifestyle factors.
Our calculator uses the 35ml per kg of body weight formula — a clinically recognised baseline recommended by the World Health Organization — and adjusts it for activity level and environment.
The 8 Glasses a Day Rule — Is It Accurate?
The popular “8 glasses a day” rule is a rough guide, but it doesn’t account for individual differences. A 50kg sedentary person has very different needs to a 90kg athlete training in summer heat. A personalised calculation is always more accurate.
Does Coffee Dehydrate You?
Caffeine has a mild diuretic effect, meaning it causes your body to lose slightly more fluid. Research published in the PLOS ONE journal suggests that while moderate coffee consumption does contribute to overall fluid intake, you should add approximately 150ml of extra water for each cup of coffee consumed to fully compensate.
How Does Climate Affect Hydration?
In hot or humid conditions, your body loses significantly more fluid through sweat. The CDC recommends increasing fluid intake by at least 300–500ml on hot days or when working in humid environments.
Signs You’re Not Drinking Enough Water
Common signs of mild dehydration include dark yellow urine, headaches, fatigue, difficulty concentrating, and dry mouth. Aim for pale yellow urine as a simple indicator of good hydration.
Frequently Asked Questions
How is my water intake calculated?
We use 35ml per kg of body weight as the base, then multiply by an activity factor (1.0–1.8). Climate and caffeine adjustments are added on top. This aligns with guidelines from the National Academies of Sciences and WHO.
Does food count toward my water intake?
Yes — roughly 20% of daily water intake comes from food, particularly fruits and vegetables. Our calculator focuses on fluid intake from drinks, which is the primary controllable factor.
Should I drink more water when exercising?
Yes. On top of your daily baseline, aim to drink an extra 400–600ml for every hour of moderate exercise. Set your activity level in the calculator to account for regular training.
Is it possible to drink too much water?
Yes — a condition called hyponatremia can occur from overhydration, though it’s rare in healthy adults. Sticking to the calculated range and drinking to thirst is safe for most people.
What is the best time of day to drink water?
Spreading your intake evenly across the day is ideal. Starting with a glass of water in the morning rehydrates you after sleep, drinking before meals aids digestion, and sipping steadily through the afternoon keeps energy levels stable.