Water Intake Calculator
Find out how much water to drink a day based on your body weight, daily exercise and the weather, shown in ounces, liters, cups and bottles.
Informational only, not medical advice. Talk to a doctor.
How it works
Enter your body weight in pounds or kilograms. The starting point is a widely used guideline: drink about half your body weight in pounds as fluid ounces each day. Someone who weighs 160 pounds starts with a base of 80 ounces, which is about 2.4 liters or 10 cups.
Add the minutes you exercise on a typical day. The calculator adds 12 ounces for every 30 minutes of activity, because sweating during a workout removes water that needs to be replaced. Long, intense sessions in the heat can need even more, so treat this as a minimum on hard training days.
Choose hot or humid weather if that matches your day. Heat raises sweat losses even when you are resting, so 16 extra ounces are added. The total is then converted to liters, 8 ounce cups and standard 16.9 ounce bottles so it is easy to plan your day.
Formula
base
Where:
- body weight
- = Your weight in pounds (kilograms are converted automatically)
- minutes
- = Exercise time on a typical day
- total
- = Estimated daily fluid goal in US fluid ounces
Worked example
A 160 pound adult who exercises for 60 minutes on a hot day starts with 160 × 0.5 = 80 ounces. Exercise adds 60 ÷ 30 × 12 = 24 ounces and the heat adds 16 ounces.
The daily goal is 80 + 24 + 16 = 120 ounces. That equals about 3.5 liters, 15 cups of 8 ounces, or a little over 7 standard 16.9 ounce water bottles spread across the day.
Tips for reaching your daily water goal
Knowing how many ounces of water you should drink a day is only half the job; the other half is building a habit. Start the morning with a full glass before coffee, keep a refillable bottle on your desk, and drink a glass with every meal. If your goal is 96 ounces, that is just under six 16.9 ounce bottles, or one bottle roughly every two to three waking hours.
Your needs change from day to day. On a rest day in cool weather you may need only the base amount, while a long run in summer heat can add a liter or more. Older adults often feel less thirst, and pregnant or breastfeeding people usually need extra fluid, so they should plan intake deliberately and follow advice from their own doctor.
Frequently asked questions
A common starting point is half your body weight in pounds as ounces of water, plus more for exercise and hot weather. A 150 pound person would aim for about 75 ounces before adding activity.
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For informational purposes only. This calculator does not provide medical advice. Consult a qualified professional before making decisions based on these results.