Water Intake Calculator
Estimate a daily fluid target from body weight, exercise, climate and caffeine intake, converted into glasses and bottles.
Daily fluid target
2.95 litres
About 12 glasses of 250 ml
Bottles (500 ml)
5.9
Per waking hour
184 ml
- Baseline for body weight
- 2.48 L
- Exercise allowance
- +0.35 L
- Climate adjustment
- +0 L
- Caffeine adjustment
- +0.12 L
- Total
- 2.95 L
- US cups (240 ml)
- 12.3 cups
How this was calculated
- 1.Baseline = 0.033 × 75 kg = 2.48 L.
- 2.Exercise adds 0.35 L per 30 minutes: 30 min → 0.35 L.
- 3.Climate (temperate) and 2 caffeinated drinks add 0.12 L.
- 4.Total ≈ 2.95 L per day, spread across the waking hours.
Includes water from all drinks and food. Around 20% of daily fluid usually comes from food. People with kidney or heart conditions should follow medical advice instead.
How the water intake calculation works
Fluid needs scale with body size, activity and environment. A widely used baseline is 33 ml per kilogram of body weight, which for a 75 kg adult gives about 2.5 litres.
Exercise adds losses through sweat — roughly 0.35 litres per half hour of moderate activity. Hot and humid conditions increase it further, while caffeine has a mild diuretic effect that slightly raises the requirement.
Thirst and urine colour remain the most reliable everyday guides. Drinking more than you need is not beneficial and, in extreme cases, can be harmful.
Worked example
75 kg, 30 minutes of exercise, temperate climate, two coffees.
- →Baseline = 0.033 × 75 = 2.48 L
- →Exercise = 0.35 L
- →Caffeine = 2 × 0.06 = 0.12 L
Answer: About 2.95 litres a day, or roughly 12 glasses.
Water Intake FAQs
Does tea or coffee count?
Yes. Tea, coffee and milk all contribute to fluid intake. The small diuretic effect of caffeine is already allowed for in this calculation.
Is eight glasses a day right?
It is a rough rule of thumb, not a scientific target. Needs vary with body size, activity and climate — which is what this calculator accounts for.
Can I drink too much water?
Yes. Very large amounts in a short time can dilute blood sodium. Spread intake through the day and follow thirst rather than forcing a number.
Water Intake Calculator is part of the health calculators collection on Calcora, alongside 7 other tools. Results are calculated in your browser and are for information only — see our disclaimer.
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