How much water should you drink a day?
Enter your weight and activity level to get an estimate of your daily water needs in liters, glasses, and bottles — with practical tips to actually hit the target.
Where this estimate comes from
The most common rule of thumb starts from body weight: roughly 30 ml of water per kilogram (about half an ounce per pound). For a 155-lb person that works out to just over 2 liters — around 70 fl oz — per day, in line with general guidance such as the U.S. National Academies' figures of about 11.5 cups of fluids a day for women and 15.5 for men from all sources. On top of that baseline you add what you lose through sweat: if you train regularly or work in the heat, you may need an extra half liter to a liter (17-34 fl oz). Fluids from tea, coffee, milk, fruit, and vegetables count too — on average they cover 20-30% of your total needs.
Easy tricks to drink more without thinking about it
Spread your water throughout the day instead of gulping it all at once: a glass right after waking up, one before every meal, and a water bottle sitting in plain sight on your desk beat any reminder app. Watch for the signs of mild dehydration: dark urine, an afternoon headache, and sudden fatigue. Thirst itself often shows up late, especially in older adults.
This tool provides estimates only and is not medical advice. If you have a kidney or heart condition, are pregnant or breastfeeding, or take diuretics, discuss your fluid intake with your doctor.