Hydration Calculator
Daily water target adjusted for exercise, heat and body size.
Enter your values
Enter the body weight in kg.
Enter the exercise time in minutes/day.
Choose one of: Temperate, Warm, Hot or humid, Cold.
Enter the bottle size in ml.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Daily water target
- 3.13 litres
- In cups (240 ml)
- 13
- Bottles per day
- 4.2
- Baseline from bodyweight
- 2.48 L
- Exercise replacement
- 0.65 L
- Climate adjustment
- 0 L
- Per waking hour (16 h)
- 195 ml
Working
- 175 kg x 0.033 = 2.48 L, + 0.65 L exercise, x 1 climate = 3.13 L
Quick answer
A common baseline is 30 to 35 ml of water per kilogram per day, plus 500 to 750 ml per hour of exercise and more in hot weather.
litres = kg x 0.033 + exercise and heat additions
At a glance
| What it does | Daily water target adjusted for exercise, heat and body size. |
|---|---|
| Category | Health |
| Inputs needed | Body weight, Exercise time, Climate, Bottle size |
| Main output | Daily water target |
| Formula | litres = kg x 0.033 + exercise and heat additions |
| Cost | Free — no sign-up, no download |
How to use the Hydration Calculator
- 1Enter your weight and typical daily exercise duration.
- 2Pick the climate you actually spend the day in, including air-conditioned or heated indoor air.
- 3Spread the total across waking hours rather than drinking it all at once.
Inputs explained
- Body weight(kg)
- Enter the body weight in kg.
- Exercise time(minutes/day)
- Enter the exercise time in minutes/day.
- Climate
- Choose one of: Temperate, Warm, Hot or humid, Cold.
- Bottle size(ml)
- Enter the bottle size in ml.
Worked example
Using the values the calculator loads with:
Inputs
- Body weight75 kg
- Exercise time60 minutes/day
- ClimateTemperate
- Bottle size750 ml
Results
- Daily water target3.13 litres
- In cups (240 ml)13
- Bottles per day4.2
- Baseline from bodyweight2.48 L
- Exercise replacement0.65 L
- Climate adjustment0 L
- Per waking hour (16 h)195 ml
- 75 kg x 0.033 = 2.48 L, + 0.65 L exercise, x 1 climate = 3.13 L
Frequently asked questions
Do tea, coffee and food count?
Yes. Food supplies roughly 20% of intake and caffeinated drinks are still net hydrating, so the target includes all fluids.
How do I know if I am drinking enough?
Pale straw-coloured urine several times a day is the practical test. Dark urine or thirst means you are already behind.
What do I need to enter into the Hydration Calculator?
Just 4 values: body weight, exercise time, climate, bottle size. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Hydration Calculator work out the answer?
A common baseline is 30 to 35 ml of water per kilogram per day, plus 500 to 750 ml per hour of exercise and more in hot weather. It applies the formula litres = kg x 0.033 + exercise and heat additions and shows the working so you can check each step by hand.
Is the Hydration Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.