Water Intake Calculator
How much water should you drink a day? Enter your weight, activity and climate and this water intake calculator estimates your daily needs in litres, cups and glasses, with a simple plan to spread it through the day.
Base water intake starts around 35 ml per kg of body weight, plus an additional 500 to 750 ml per hour of vigorous exercise, and extra in hot or humid climates. Aim to spread your hydration steadily throughout the waking day.
Recommended Daily Water Intake
13.1 Glasses (8 oz)Covers total daily hydration needs from water and beverages based on your body weight, activity sweat rate, and ambient climate.
Standard Cups
12.4 cups
250 ml each
Hourly Sip Rate
~207 ml / hr
Across 15 waking hours
Food Moisture
~20%
Typical diet contribution
Hourly Drinking Schedule
| Time Window | Target Volume | Hydration Focus |
|---|---|---|
| Morning (7:00 AM – 11:00 AM) | 828 ml | Hydrate early after overnight fluid loss |
| Midday (11:00 AM – 3:00 PM) | 828 ml | Sip consistently around meals and workout |
| Late Afternoon (3:00 PM – 7:00 PM) | 828 ml | Replace workout sweat and afternoon fatigue |
| Evening (7:00 PM – 10:00 PM) | 621 ml | Taper down to prevent frequent nighttime waking |
Drinking steadily across the day prevents acute gastric fullness and promotes cellular hydration.
100% Device-Local
Inputs never leave your browser
Instant Live Maths
Calculates in real time as you type
Clinical Equations
WHO, CDC, ACSM & Mifflin-St Jeor
Suggest a Feature or Improvement for Water Intake Calculator
Need custom options, higher limits, or extra format support? Let our engineering team know!
How to use Water Intake Calculator
- 1Enter your body weight in kilograms or pounds.
- 2Input your expected daily exercise duration in minutes.
- 3Select your climate condition (temperate, hot/humid, or cold/dry).
- 4View your recommended total fluid target in litres, fluid ounces, and standard 250ml glasses, accompanied by a realistic daytime sipping schedule.
Why hydration matters for performance
A dehydration level of just 2% of body weight significantly impairs cognitive focus, reduces strength and power output, and elevates cardiovascular strain during aerobic workouts.
Your total fluid intake includes drinking water, herbal teas, coffee, and moisture naturally present in fresh fruits and vegetables (which typically supply about 20% of your daily water).
Frequently Asked Questions
Is 8 glasses of water a day right?
The '8x8 rule' is an oversimplified guideline. Actual hydration needs vary significantly with body weight, ambient temperature, humidity, and physical activity levels.
Does tea or coffee count toward water intake?
Yes. While caffeine exhibits a mild diuretic effect in non-habitual consumers, caffeinated beverages still contribute positively to overall daily net hydration.
How much water should I drink when exercising?
Drink approximately 400 to 800 ml per hour of exercise, sipping 150 to 250 ml every 15 to 20 minutes depending on your sweat rate and heat index.
Can you drink too much water?
Yes. Drinking massive volumes of plain water in a short window without electrolytes can trigger hyponatremia (water intoxication), diluting blood sodium to dangerous levels. Always pace your fluid intake throughout the day.
Related Calculators
Calorie Calculator
Calculate your daily calorie needs for weight loss, maintenance, or muscle gain.
Macro Calculator
Calculate your daily macronutrients (protein, carbs, and fat) for weight loss or muscle building.
Running Pace Calculator
Calculate pace, time, or distance for running with splits for 5K, 10K, half marathon, and marathon.
TDEE Calculator
Estimate your Total Daily Energy Expenditure and discover your true maintenance calories.
Scientific Sources & Evidence
- World Health Organization (WHO) — Body Mass Index Classification
- CDC Growth Charts — BMI-for-age LMS Percentiles
- Mifflin et al. (1990) — Basal Metabolic Rate Predictive Equations
- NICE Guideline NG246 — Identification and Management of Overweight and Obesity
- American College of Sports Medicine (ACSM) — Exercise Testing & Prescription
- European Food Safety Authority (EFSA) — Dietary Reference Values for Water