Daily Water Intake Calculator
Free Daily water intake Calculator for human physiology. Enter variables to compute results with formulas and detailed steps.
Reviewed by Daniel Agrici, Founder & Lead Developer
Formula
Water (mL) = (Weight x 35) + Activity Adjustment + (Exercise min / 30 x 400) x Climate Factor
Where Weight is in kilograms, the base rate of 35 mL/kg comes from EFSA guidelines. Activity adjustment adds 0-1,400 mL based on daily activity. Exercise adds approximately 400 mL per 30 minutes. Climate factor ranges from 0.9 (cold) to 1.35 (very hot) to account for increased sweat losses.
Worked Examples
Example 1: Office Worker in Temperate Climate
Problem:A 75 kg person with a sedentary office job in a temperate climate who walks for 30 minutes daily.
Solution:Base intake: 75 kg x 35 mL/kg = 2,625 mL\nActivity (sedentary): +0 mL\nExercise (30 min): +(30/30) x 400 = +400 mL\nClimate (temperate): x 1.0\nTotal = (2,625 + 0 + 400) x 1.0 = 3,025 mL\nAbout 20% from food: 605 mL\nFrom drinks: 2,420 mL (about 10 glasses)
Result:Total: 3,025 mL (3.0 L) = ~10 glasses of 250 mL
Example 2: Active Person in Hot Climate
Problem:An 85 kg person who exercises 60 minutes daily in a hot climate with an active lifestyle.
Solution:Base intake: 85 kg x 35 mL/kg = 2,975 mL\nActivity (active): +1,050 mL\nExercise (60 min): +(60/30) x 400 = +800 mL\nClimate (hot): x 1.2\nTotal = (2,975 + 1,050 + 800) x 1.2 = 5,790 mL\nAbout 20% from food: 1,158 mL\nFrom drinks: 4,632 mL (about 19 glasses)
Result:Total: 5,790 mL (5.8 L) = ~24 glasses of 250 mL
Frequently Asked Questions
How much water should I drink per day?
The general recommendation is approximately 35 mL per kilogram of body weight per day, though individual needs vary significantly. The U.S. National Academies of Sciences recommends about 3.7 liters (125 oz) for men and 2.7 liters (91 oz) for women from all beverages and food combined. About 20% of daily water intake comes from food, especially fruits and vegetables. Actual needs depend on body size, activity level, climate, and health status. Thirst is generally a reliable indicator, though it may lag in older adults or during intense exercise.
Does exercise increase water needs?
Yes, exercise significantly increases water needs. During moderate exercise, you can lose 0.5-1 liter of water per hour through sweat. Intense exercise in hot conditions can cause losses of 1-2.5 liters per hour. The American College of Sports Medicine recommends drinking 400-600 mL (14-20 oz) 2 hours before exercise, 150-350 mL every 15-20 minutes during exercise, and 450-675 mL for every 0.5 kg of body weight lost after exercise. For exercise lasting over 60 minutes, sports drinks with electrolytes help replace sodium lost through sweat.
Can you drink too much water?
Yes, overhydration (hyponatremia) is a real but uncommon condition where blood sodium levels drop dangerously low from excessive water intake. It most commonly occurs in endurance athletes who drink large amounts of water without replacing electrolytes. Symptoms include nausea, headache, confusion, and in severe cases, seizures. Generally, healthy kidneys can process about 800-1,000 mL per hour. As a rule, you should not drink more than 1 liter per hour. Spreading intake throughout the day rather than consuming large amounts at once is recommended.
Does climate affect water requirements?
Climate has a major effect on water needs. In hot, humid environments, sweat rates increase dramatically and water needs can rise by 20-35% or more. At high altitudes (above 2,500 meters), increased respiration and dry air accelerate water loss, requiring an additional 1-1.5 liters per day. Even cold, dry winter air increases respiratory water loss. Air-conditioned environments can be dehydrating due to low humidity. Travelers to new climate zones should consciously increase water intake for the first few days to allow acclimatization.
References
Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy