Water Intake Calculator
Staying hydrated supports focus, energy, and recovery — especially on long desk days. Enter your weight and activity level for a daily water target in liters and cups.
Most people drink barely half this without noticing. Even mild dehydration quietly saps focus and energy — keep a bottle in sight and sip through the day.
A general guide based on body weight and activity. Hot weather and intense exercise increase your needs.
How it's calculated
Daily water (ml) = body weight (kg) × 33 + activity adjustment
A common starting point is roughly 33 ml of water per kilogram of body weight, plus extra for how active you are. It is a sensible baseline, not a hard rule — hot weather, illness, and intense exercise all raise your needs, while food (especially fruit and vegetables) contributes water too.
What your result means
Added on top of the weight-based baseline, matching the activity levels in the calculator.
| Activity level | Added water | Who it fits |
|---|---|---|
| Mostly sitting | +0 ml | A typical desk day with little exercise — the baseline target. |
| Some activity | +350 ml | Light workouts, walking, or being on your feet for part of the day. |
| Active / exercise | +700 ml | Regular training, manual work, or hot conditions that increase sweat loss. |
How much water you actually need
The old 'eight glasses a day' rule is a rough average, not a personal target. Scaling to body weight gets you closer, because a larger body simply needs more. Treat the result as a starting guide and adjust up on hot days, during exercise, or whenever you feel thirsty.
Signs you are not drinking enough
Dehydration rarely announces itself dramatically. The everyday signs are subtle — afternoon fatigue, trouble concentrating, headaches, and dark yellow urine. On a busy desk day it is easy to miss all of them, which is why mild dehydration is so common among people who sit and work.
Easy ways to drink more at a desk
Keep a filled bottle within sight — visibility is the single best reminder. Pair sips with existing habits like sending an email or finishing a meeting, and front-load earlier in the day so you are not playing catch-up (and disrupting sleep) at night. Hydration is one small piece of building healthy phone habits and a better desk day.
Frequently asked questions
How much water should I drink a day?
A common starting point is about 30 to 35 ml per kilogram of body weight, adjusted up for activity and hot weather. For many adults that lands between 2 and 3 liters, but thirst and urine color are good real-time guides.
How do I calculate water intake by weight?
Multiply your weight in kilograms by roughly 33 to get a baseline in milliliters, then add more for exercise and heat. This calculator does that for you and converts the result into liters and cups.
Do coffee and tea count toward water intake?
Mostly, yes. Despite their mild diuretic effect, the fluid in coffee and tea still contributes to your daily total. Water is the better default, but everyday caffeinated drinks are not the dehydrators they are often made out to be.
What are the signs of dehydration?
Thirst, dark yellow urine, tiredness, headaches, and difficulty concentrating are the common early signs. On long desk days these are easy to mistake for an ordinary afternoon slump, so a glass of water is often worth trying first.
Can you drink too much water?
It is rare, but drinking very large amounts in a short time can dangerously dilute your blood sodium. Spreading intake across the day and drinking to thirst keeps you well clear of any risk.
Does activity change how much water I need?
Yes. Exercise and heat increase water lost through sweat, so active days and hot weather both raise your needs. Add roughly an extra glass or two around workouts, and more if you are sweating heavily.