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Water Intake Calculator: How Much Water Should I Drink?

Calculate how much water to drink per day based on your weight, exercise and climate, in fluid ounces or liters.

Calculate your daily water

Switch units with the lb/ft – kg/cm toggle at the top of the page. Nothing you enter leaves your device.

How much water do you really need?

The U.S. National Academies of Sciences, Engineering, and Medicine suggest an adequate total daily fluid intake of about 3.7 liters (125 oz) for men and 2.7 liters (91 oz) for women, from all drinks and food. About 20% usually comes from food such as fruit, vegetables and soups. Needs go up with body size, exercise, heat and altitude.

How this calculator works

We start at about 33 ml per kg of body weight, add about 350 ml (12 oz) for every 30 minutes of exercise, and add 500 ml (17 oz) for hot or humid weather. It is a practical starting point, not a strict rule.

Signs you are well hydrated

  • Pale yellow urine
  • Rarely feeling thirsty
  • Steady energy during workouts

Hydration tips for training

  • Drink a glass of water 1–2 hours before training.
  • Sip during workouts, especially in heat.
  • For sessions longer than 60–90 minutes in hot conditions, consider a drink with electrolytes.
  • Do not force down huge amounts of water. Drinking far too much in a short time can be dangerous (hyponatremia).

How to use your result

A calculator gives you a starting point, not a final answer. The most reliable way to use any fitness number is the measure → act → review loop:

  1. Measure: record your result today, along with your morning body weight, waist measurement and a few photos.
  2. Act: follow a matching plan for 2–4 weeks. Use the plan builder to get a workout program and a 7-day meal plan that fit your numbers.
  3. Review: compare your weekly averages and measurements. If things are moving in the right direction at a sustainable pace, keep going. If not, adjust by small amounts (100–200 calories, one extra workout, 2,000 extra steps) and review again.

US and metric units

Every HelloMyTrainer calculator works in both systems. Use the lb / ft or kg / cm switch at the top of the page; your choice is remembered on this device for all calculators and meal plans. Useful conversions: 1 kg = 2.2 lb, 1 inch = 2.54 cm, 1 foot = 30.48 cm, 1 liter = 33.8 US fluid ounces.

Who should be careful with these numbers

These calculators are designed for healthy adults aged 18 and over. They are not suitable for children or teenagers, pregnant or breastfeeding women, people with a history of eating disorders, competitive athletes with very high muscle mass, or people with medical conditions that affect weight, metabolism or fluid balance (such as heart failure, kidney disease or thyroid disorders). If any of these apply to you, please speak with your doctor or a registered dietitian before using the results.

Your privacy

We never ask for your name, email or any personal details to use our tools. The calculations run in your web browser and the numbers you type are not sent to our servers. See our Privacy Policy for details.

Frequently asked questions

Do coffee and tea count?

Yes. Moderate amounts of coffee and tea contribute to your daily fluid intake.

Does water help with weight loss?

Drinking water before meals can help some people feel fuller and eat less, and replacing sugary drinks with water cuts calories.

Can I drink too much water?

Yes, in extreme cases. Spread intake through the day and follow your thirst.

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Results are estimates for healthy adults and are not medical advice.