1. Enter your weight
Type your weight and pick kg or lb. Body size is the biggest factor in daily fluid needs.
Free online tool
Daily water intake calculator.
Enter your weight, pick your activity level, and get a daily water target in liters, glasses, and ounces — right in the browser. When you want reminders, widgets, and Apple Watch logging to actually hit that target, BigDrink keeps you on track.
How to use it
How to use the calculator.
Three inputs, instant answer. The formula uses about 35 ml per kilogram of body weight plus an activity bonus.
2. Pick your activity level
Choose how much you exercise on a typical day. Sweat loss adds roughly 350–700 ml to your baseline.
3. Spread it across the day
Drink steadily rather than all at once — a glass with each meal and around workouts covers most of the target.
FAQ
Frequently asked questions.
Quick answers about this tool and how to train with it.
How much water should I drink a day?
A practical estimate is about 35 ml per kilogram of body weight — roughly 2.4 liters for a 70 kg adult — plus 350–700 ml on days you exercise. Common general references land in the same range: about 3.7 liters of total fluids per day for men and 2.7 liters for women, which includes water from food.
Does coffee or tea count toward my water intake?
Yes — despite the caffeine, coffee and tea contribute net fluid. Water is still the best default because it adds no sugar or calories, but your morning coffee counts toward the total.
Can I drink too much water?
It's rare but possible — drinking many liters in a short window can dilute blood sodium (hyponatremia). Spread intake across the day, and let thirst and pale-yellow urine be your feedback signals.
How do I actually remember to drink enough?
Tie drinking to existing habits (meals, breaks, workouts) and make the target visible. BigDrink does exactly this on Apple devices: smart reminders, home screen widgets, Apple Watch one-tap logging, and iCloud sync across iPhone, iPad, Mac, and Apple Vision.
Knowing your number is easy. Hitting it daily is the hard part.
BigDrink turns your water target into a habit with reminders, widgets, Apple Watch logging, and HealthKit sync — free on the App Store.