onlinecalculator.me

Free online daily water intake calculator

How much water should you drink per day? This calculator estimates your daily hydration target from body weight, activity level, and climate using a weight-based formula.

Units
Liters
—
L / day
Fluid oz
—
fl oz / day
Cups
—
8 oz cups / day
Milliliters
—
mL / day
About this calculator

How to use

  1. Choose Imperial or Metric with the unit toggle.
  2. Enter your body weight.
  3. Select your typical activity level from the dropdown.
  4. If you live or work in a hot or humid environment, select Hot climate.
  5. Your daily water target appears in four unit formats.

The formula

Base = weight (kg) × 35 mL
Adjusted = Base × activity multiplier
Final = Adjusted + climate addition

Activity multipliers:

LevelMultiplier
Sedentary1.00 ×
Light1.10 ×
Moderate1.20 ×
Active1.35 ×
Very active1.50 ×

Hot climate adds 500 mL to the final total.

Worked example

Person weighing 70 kg, moderately active, temperate climate:

Base  = 70 × 35 = 2,450 mL
Adjusted = 2,450 × 1.20 = 2,940 mL
Final = 2,940 mL = 2.94 L = 99.4 oz ≈ 12.4 cups

Same person in a hot climate:

Final = 2,940 + 500 = 3,440 mL = 3.44 L

Notes

  • Sources: National Academies of Sciences (2004). Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. NAP. Weight-based guideline (35 mL/kg): Mayo Clinic hydration guidance.
  • These values are general targets. Individual needs vary with sweat rate, diet, medications, and health conditions. People with kidney disease, heart failure, or other medical conditions should follow clinician guidance.

Frequently asked

How much water should I drink per day?
A common clinical guideline is 35 mL per kilogram of body weight as a baseline, adjusted upward for physical activity and hot climates. For a 70 kg person with moderate activity in a temperate climate, that comes to roughly 2.9 liters (about 98 oz) per day. The National Academies of Sciences set general adequate intake levels of 3.7 L/day for men and 2.7 L/day for women, which includes water from all foods and beverages.
Does coffee, tea, or juice count toward my daily water intake?
Yes. Despite the mild diuretic effect of caffeine, research shows that caffeinated beverages still contribute net fluid. The Institute of Medicine includes all beverages — coffee, tea, juice, and milk — in daily fluid totals. Plain water is still the best default, but a morning coffee counts.
What are the signs of dehydration?
Early signs include thirst, dark yellow urine, dry mouth, and mild fatigue. More pronounced dehydration causes headache, dizziness, decreased concentration, and reduced physical performance. A simple check: urine should be pale yellow (like lemonade), not dark amber. Severe dehydration requires medical attention.
Why does a hot climate increase my water needs?
Heat and humidity increase sweat rate significantly — up to 1–2 liters per hour during strenuous activity in hot conditions. Even at rest, a hot environment raises insensible fluid losses through the skin. This calculator adds approximately 500 mL for hot or humid climates as a conservative baseline adjustment.
Can I share my results with a link?
Yes. Click "Share with my numbers" to copy a URL with your weight, activity level, and climate encoded as query parameters. Anyone who opens it will see the same inputs and results.