Hydration Guides

Most water advice is a round number with no explanation. These guides show the math, link to where each figure comes from, and say plainly when the evidence is thin. Pick your question, then run the matching calculator.

Find your number

Start here if you want a daily target and want to know where it comes from.

• Water Intake by WeightA chart from 100 to 250 lb in ounces, liters and cups, built with the same formula as the calculator.
• Water Intake Formulas ComparedHalf your body weight in ounces, 30 to 35 mL per kg and the National Academies figures, side by side.
• Is 64 oz of Water a Day Enough?Where the 8 glasses idea came from and how 64 oz compares with your size.

What counts as water

Not every drink works the same way.

• What Counts as Water IntakeCoffee, tea, sparkling water, milk and food, and what studies found about each.

Too much, too little, too many trips

When the number feels off.

• How Much Water Is Too Much?How overhydration happens, who is at higher risk, and when to see a doctor.
• Is a Gallon of Water a Day Too Much?Who a gallon fits, who it does not, and why speed matters.
• Why Do I Pee So Much When I Drink Water?The usual reason, other causes, and warning signs.

Training and supplements

For people who sweat or take creatine.

• Does Creatine Make You Retain Water?What the research says about early weight gain and where the water goes.
• Do You Need Electrolytes?When plain water is enough and when electrolytes may help.

Calculators

When you want a number for your own weight and activity.

• Daily Water Intake CalculatorYour daily target from weight and exercise.
• Water Bottles Per Day CalculatorTurn a goal into bottles and drink-by times.
• How Many Bottles of Water Are in a Gallon?Convert gallons, liters or ounces into bottles.
• Creatine Water Intake CalculatorA water number for maintenance or loading.
• Sweat Rate CalculatorWeigh yourself before and after a workout to find liters per hour.
• Water Intake Calculator for Weight LossA daily target plus the before-meal plan used in two trials.
• Pregnancy Water Intake CalculatorThe National Academies figures for pregnancy and breastfeeding.
• All Water CalculatorsEvery calculator on one page, grouped by what you need.

General information for healthy adults, not medical advice. If you are pregnant or breastfeeding, or you have kidney, heart or liver conditions or a fluid limit, ask a clinician first. Terms and medical disclaimer.