Water Intake Calculator
How much to actually drink, adjusted for your weight, training and climate. Not a flat eight glasses for everybody.
Drink about
2.8 liters a day
95 fl oz, or about 12 glasses of 8 oz
Baseline
2.5 L
From body weight
Exercise
+0.4 L
About 17 oz per hour
Climate & other
+0.0 L
Heat, pregnancy
This is water to drink, not total intake. Around 20% of your fluid arrives in food, and tea, coffee and milk all count toward the rest. The simplest check is urine color: pale straw is right, dark amber means drink more, and completely clear means you can ease off.
Where the number comes from
The baseline here is about 35 ml per kilogram of body weight, a figure used clinically for adults. It scales sensibly, which matters: a 130 lb person and a 220 lb person do not need the same amount of water, and most rules of thumb ignore that completely. Exercise adds roughly 17 oz per hour, heat multiplies the total, and pregnancy or breastfeeding add a fixed amount on top.
For context, the US National Academies put adequate total water intake at 3.7 liters a day for men and 2.7 for women. Those numbers include food and every other drink. Since roughly a fifth of your intake arrives as food, the amount you need to drink is lower, which is what this calculator reports.
None of this is precise, and it does not need to be. Thirst is a well-calibrated mechanism in healthy adults, and your kidneys handle a wide range of intakes without complaint. A target is mostly useful for catching the days you are too busy to notice you are thirsty.
Daily water intake by body weight
Baseline needs before exercise or heat is added. If you train hard or live somewhere warm, expect to sit above these numbers.
| Body weight | Liters | Fluid ounces | 8 oz glasses |
|---|---|---|---|
| 110 lb (50 kg) | 1.8 L | 59 oz | 7 |
| 132 lb (60 kg) | 2.1 L | 71 oz | 9 |
| 154 lb (70 kg) | 2.5 L | 83 oz | 10 |
| 176 lb (80 kg) | 2.8 L | 95 oz | 12 |
| 198 lb (90 kg) | 3.1 L | 107 oz | 13 |
| 220 lb (100 kg) | 3.5 L | 118 oz | 15 |
| 243 lb (110 kg) | 3.9 L | 130 oz | 16 |
What counts and what doesn’t
Counts
- Water and sparkling water
- Tea and coffee, yes really
- Milk and plant milks
- Juice, soup, broth
- Fruit and vegetables. Cucumber, watermelon and lettuce are over 90% water.
Works against you
- Alcohol, which suppresses vasopressin and causes a net loss
- Very high sodium meals, which raise fluid needs
- Illness with vomiting or diarrhea, where electrolytes matter too
- Long-haul flights, since cabin humidity is extremely low
Signs you are behind
Mild dehydration is common and rarely announces itself as thirst. Losing even 1 to 2% of body weight in fluid measurably reduces concentration, mood and exercise performance.
Early signs
- Dark yellow urine, or going hours without needing to
- A dull afternoon headache
- Dry mouth and lips
- Feeling tired without a clear reason
- Hunger shortly after eating
Get help for
- Dizziness on standing that does not pass
- A racing heartbeat at rest
- Confusion or unusual irritability
- No urination for 8 hours or more
- Skin that stays tented when pinched
The right-hand column matters most for older adults and young children, where thirst is a less reliable signal and dehydration develops faster.
Hydration around training
Sweat rates vary enormously, from about half a liter an hour in a cool gym to well over two liters an hour cycling in the heat. Any per-hour guideline is an average across a very wide range, which is why the weigh-in method beats it.
Weigh yourself before and after a session, without clothes, and drink about 24 oz for every pound lost. Do it two or three times and you will know your own sweat rate better than any chart can tell you. A loss of more than 2% of body weight during a session means you went in underhydrated, drank too little during it, or both.
Sodium is the part people skip. Sweat carries roughly 1 g of sodium per liter, so long or hot sessions lose meaningful amounts. If you finish a workout with a headache despite drinking plenty, salt is the usual culprit rather than water.
Hitting the target without thinking about it
Anchor it to things you already do. A glass with each meal, one when you wake up and one before bed covers most of the target with no willpower involved.
Use one bottle whose size you know. Three refills of a 24 oz bottle is far easier to keep track of than counting glasses through the day.
Spread it out. Front-loading the whole day into the evening mostly produces interrupted sleep. Aim to have two thirds of it in by mid-afternoon.
Eat your water. Soups, fruit and salads contribute a surprising amount, which is one reason people find hydration easier on a produce-heavy diet.
Make it taste of something. Lemon, cucumber, mint or a splash of juice all help if plain water bores you. Flavored water you drink beats plain water you do not.