Water Intake Calculator
There's no universal 'eight glasses' rule — fluid needs scale with body mass, activity, climate, and life stage. This tool starts from ~30 ml/kg of body weight for sedentary adults and adjusts: +5 ml/kg per activity level, +500 ml for hot climate, −100 ml for cold, +300 ml for pregnancy, +700 ml for breastfeeding. Returns daily total in liters, ml, fl oz, glasses (240 ml), and bottles (500 ml) — plus a suggested 4-block intake schedule across the day.
Daily target
2.45 L
2450 ml · 83 fl oz · 10 glasses (240 ml) · 4.9 bottles (500 ml)
Suggested schedule
Morning
735 ml
6:00 – 11:00
Midday
735 ml
11:00 – 14:00
Afternoon
613 ml
14:00 – 18:00
Evening
368 ml
18:00 – 21:00
Guidelines vary by source (US IOM, EFSA, WHO). This calculator uses ~30 ml/kg as a baseline and adds adjustments. Listen to thirst, watch for dark-yellow urine.
How to use
- Enter your weight and choose units.
- Pick your typical activity level and current climate.
- Check pregnancy / breastfeeding if applicable. Read your daily target and time-block schedule.
Frequently asked questions
- Does coffee/tea count toward intake?
- Mostly yes. Older advice about caffeine being a net diuretic doesn't hold for moderate intake — coffee, tea, milk, juice all contribute. Water from food (fruit, soup) is also real, accounting for ~20% of daily fluid in most diets.
- Why so much for breastfeeding?
- Lactation produces ~750 ml of milk/day on average, which has to come from somewhere. Guidelines (US IOM, EFSA) add ~700 ml above non-pregnant baseline. Acute thirst is also a good cue — drink to it.
- Can I drink too much water?
- Yes — hyponatremia (low blood sodium) happens at extreme intake, typically > 1 L/h sustained for hours. Healthy kidneys handle up to ~0.8–1 L/h. Don't force-drink past thirst during long exercise.
- Why does it lock at 1L minimum?
- Even very small adults shouldn't go below ~1 L/day from fluid alone. The calculator clamps the floor so low-weight inputs don't produce dangerous targets.
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