Water Intake Calculator
Not sure how much water you need? Enter your weight, activity, and climate and you will get a daily target in liters. Stay hydrated without guessing.
TL;DR
- Your water need depends on weight, activity, and temperature
- Hydration Calculations: Water Intake (ml) = [ Weight (kg) × 35 ] + Activity Bonus + Climate Bonus
- Example 1: Active adult hydration requirements
How it works
Your water need depends on weight, activity, and temperature. Bigger bodies and harder workouts need more fluid.
The math
Start with weight times 35 ml, then add for activity and climate. The total stays above 1 liter.
A base of 35 ml of water per kg of body weight, plus 400 ml for moderate activity, 800 ml for intense activity, 600 ml in hot climates, and -200 ml in cold climates. The total never drops below 1 liter.
Examples
Example 1: Active adult hydration requirements
- Weight: 75 kg, Activity: intense, Climate: hot
- Calculate base intake: 75 × 35 = 2,625 ml
- Add activity bonus: 2,625 + 800 = 3,425 ml
- Add hot-climate bonus: 3,425 + 600 = 4,025 ml
- Result: Recommended daily intake is approximately 4.0 liters of water.
When to use it
✦ Athletic Conditioning and Recovery
Manage hydration before, during, and after exercise to prevent performance drops and muscle cramps.
✦ Workplace Productivity and Focus
Maintain proper hydration to prevent fatigue and headaches during long working hours.
✦ Weight Loss and Satiety Management
Drink water before meals to assist with portion control and metabolic processes.
⚠ Common mistakes
- Waiting Until Thirsty: Thirst is a late-stage sign of mild dehydration; drink consistently throughout the day.
- Over-hydration: Consuming excess water too quickly can lead to hyponatremia, where sodium levels in the blood drop dangerously low.
FAQ (6)
Do other beverages count toward hydration?
Yes, herbal teas and water-rich foods (fruits, vegetables) contribute toward daily fluid goals.
How do I check if I am hydrated?
The easiest way is to check urine color: a pale, straw-like color indicates optimal hydration.
What happens to my weight, height or other health data?
It never leaves your phone. BMI, BMR, body-fat — all computed on-device, no upload, no account. That's intentional for health data: you can check a BMI of 22.8 or a TDEE of 2,100 kcal without worrying about a server log. Closing the tab clears the form from memory.
Does it work offline at the gym or on a plane?
Yep. Once the page has loaded, the calculators are fully offline-first. I've used the pace and BMI tools in airplane mode between flights — no spinner, no retry, just instant numbers. Same for sleep cycles if you're planning a shift.
Can my doctor rely on these numbers?
They're solid estimates using published formulas (WHO for BMI, Mifflin-St Jeor for BMR, CKD-EPI for GFR) but they're not a diagnosis. Think of them as a conversation starter: good for tracking trends, but your GP or nephrologist should interpret GFR, heart age or pregnancy dates with labs and context. We link the sources at the bottom for that reason.
How can I share my result with a trainer or doctor?
Use 'Share Link' in the results panel. It builds a URL with your inputs — for example BMI 70kg/175cm — so they see exactly what you entered. No data is stored on our side, the link just carries the numbers.
Sources & References
⚠ Health Disclaimer
This tool provides estimates for informational purposes only and does not constitute medical, veterinary, or professional advice. Always consult a qualified healthcare professional before making decisions about your health or treatment.