Even mild dehydration costs you strength, focus and endurance — studies link a 2% drop in body water to a clear fall in physical and mental performance. This calculator estimates how much water you should drink each day from your body weight and how much you train.
Water Intake Calculator
Estimate only — not medical advice.
How the Water Intake Calculator Works
The widely used starting point is 35 ml of water per kilogram of body weight per day. Exercise adds sweat losses, so the calculator adds 350 ml for every 30 minutes of training. Hot weather, heavy sweating and large body size all push your real need higher — treat the result as your minimum target, not a ceiling.
Worked Example
An 80 kg person who trains for 60 minutes: base = 80 × 35 = 2,800 ml, exercise = 700 ml, total = 3.5 litres a day — about 14 standard 250 ml glasses.
Signs You Are Drinking Enough
- Your urine is pale yellow most of the day (dark = drink more)
- You rarely feel very thirsty
- Your training performance and focus stay steady late in the day
Frequently Asked Questions
Does tea and coffee count toward my water intake?
Yes. Despite the mild diuretic effect of caffeine, normal cups of tea and coffee are net hydrating and count toward your daily total.
Can I drink too much water?
It is possible but rare — it mainly happens when people force down very large volumes quickly during endurance events. Drinking to this target, spread across the day, is safe for healthy adults.
How much extra water do I need in hot weather?
Add roughly 500 ml for every hour spent working or training in serious heat, and more if your clothes are soaked with sweat.
Should I drink water during workouts?
Yes — small amounts regularly. A practical guide is 150–250 ml every 15–20 minutes during hard training.