Free · No sign-up · Client-side, nothing is uploaded
Water Intake Calculator
Estimate how much water you should drink each day, personalized to your body weight, activity level, climate, and life stage.
Quick answer
Most adults need roughly 2.2 to 3.7 liters (about 74 to 125 fluid ounces) of total water per day, and this range shifts with body weight, activity, climate, and pregnancy or breastfeeding status. A simple starting formula is 30 to 35 milliliters of water per kilogram of body weight, then add more for exercise, heat, or nursing. Thirst, urine color, and how you feel are still the best day-to-day guides on top of any number.
Your personalized breakdown
Once you calculate above, this section explains exactly how your number was built, step by step.
Run the calculator above to see a personalized, plain-English breakdown of your result — your baseline from body weight, plus adjustments for activity, climate, and any other factors you selected.
How this calculator works
This tool builds your target in five transparent steps rather than showing one unexplained number. Each step uses a fixed, stated rule so you can see exactly where the total comes from.
-
Set a baseline from body weight
We multiply your body weight by 33 milliliters per kilogram, the midpoint of the commonly cited 30–35 ml/kg range used in general hydration guidance. This is the largest component of your total.
-
Apply a small sex and age adjustment
Average body composition differs slightly by biological sex and shifts somewhat after age 65, so we apply a modest ±3% adjustment to the baseline rather than a large fixed offset.
-
Add for activity
Each minute of light, moderate, or intense exercise adds 6, 10, or 14 milliliters respectively, reflecting typical sweat loss during that intensity of activity. Sedentary days add nothing here.
-
Add for climate
Hot or humid conditions add 500 ml to account for extra sweat loss; high altitude adds 250 ml to account for increased respiratory water loss and fluid turnover.
-
Adjust for pregnancy, breastfeeding, coffee, and alcohol
Pregnancy adds 150–450 ml depending on trimester, and breastfeeding adds 550–700 ml depending on stage. Coffee beyond two cups a day adds a small 50 ml offset per extra cup, and each alcoholic drink adds 100 ml to help offset its diuretic effect.
Daily water intake by weight and activity level
Prefer a quick lookup instead of the form? These general reference values use the same baseline formula at a mid-range activity add-on, without your personal adjustments.
| Body weight | Sedentary | Moderately active | Very active |
|---|---|---|---|
| 50 kg (110 lb) | 1.7 L | 2.2 L | 2.7 L |
| 60 kg (132 lb) | 2.0 L | 2.5 L | 3.0 L |
| 70 kg (154 lb) | 2.3 L | 2.8 L | 3.3 L |
| 80 kg (176 lb) | 2.6 L | 3.1 L | 3.6 L |
| 90 kg (198 lb) | 3.0 L | 3.5 L | 4.0 L |
| 100 kg (220 lb) | 3.3 L | 3.8 L | 4.3 L |
Frequently asked questions
Straight answers to the questions people ask most often about daily water needs.
How much water should I drink based on my weight?
A widely-cited starting point is about 30 to 35 milliliters of water per kilogram of body weight per day. For a 70 kg (154 lb) adult, that works out to roughly 2.3 to 2.5 liters, or about 78 to 84 fluid ounces. This is a baseline before adjusting for activity, climate, and other factors, so most people need somewhat more.
Is 8 glasses a day accurate?
The "8 glasses a day" rule (about 1.9 liters) is easy to remember but not personalized, so it undershoots for larger or more active people and overshoots for smaller, sedentary people. Actual needs vary with body weight, activity level, climate, and health status. A weight-based formula, like the one this calculator uses, gives a closer estimate than a flat rule.
How much more water do I need in hot or humid weather?
Heat and humidity increase fluid loss through sweat, so most guidance suggests adding roughly 500 milliliters (about 16 fluid ounces) to your daily baseline in hot or humid conditions. If you're also exercising outdoors in the heat, add further for exercise on top of the climate adjustment. Increase intake gradually and watch for signs of dehydration such as dark urine or persistent thirst.
How much water should I drink while pregnant or breastfeeding?
General guidance suggests pregnant people add roughly 150 to 450 milliliters (about 5 to 15 fluid ounces) to their baseline, increasing gradually through the trimesters. Breastfeeding increases fluid needs more substantially, often by around 700 milliliters (about 24 fluid ounces) per day, especially in the first six months. These are general estimates; a prenatal or postnatal care provider can give guidance tailored to your situation.
Does coffee count toward daily water intake?
Yes, in moderate amounts coffee and other caffeinated drinks do contribute to hydration; the old idea that caffeine causes a fluid deficit is largely outdated for habitual, moderate drinkers. Above roughly two to three cups a day, caffeine's mild diuretic effect becomes more noticeable, so this calculator adds a small offset only beyond that point. Water is still the most efficient way to hydrate.
How much water should I drink when exercising?
A common guideline is to add roughly 350 to 700 milliliters (about 12 to 24 fluid ounces) of water for every 30 to 60 minutes of moderate to intense exercise, on top of your baseline. Longer or more intense sessions, especially in heat, call for more. Weighing yourself before and after a workout can help you fine-tune replacement for your own sweat rate.
Can I drink too much water?
Yes. Drinking far more water than your body can process, especially in a short period, can dilute sodium levels in the blood and cause a rare but serious condition called hyponatremia. This is uncommon in everyday life but has occurred in endurance athletes and during water-drinking competitions. If you have kidney, heart, or liver conditions, talk to a doctor before making significant changes to your fluid intake.