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Water Intake Calculator
Set a daily water target from your body weight (≈ 33 mL/kg — the 30–35 mL/kg bodyweight method), plus activity (≈ 12 mL per exercise minute) and a hot/humid climate uplift (+15%), shown in mL, litres and fl oz with a base/activity/climate breakdown. Busts the "8 glasses a day" myth (needs scale with weight, activity and climate) and adds NASEM total-vs-beverage context (~20% of water comes from food, so their ~3.7 L men / 2.7 L women totals look larger). General hydration guidance, not medical advice — the real check is pale-straw urine and drinking to thirst. Accurate, instant and free — for United States.
What these mean:
What these mean:
Your daily water target is ≈ 2.9 L (2850 mL, ~96 fl oz) — base 2310 mL + activity 540 mL. That's beverage water; counting ~20% from food, your total-water need is a little higher. General hydration guidance, not medical advice.
Daily water target
2850 mL · 96 fl oz
Base (bodyweight)
2310 mL
Activity
540 mL
Climate
0 mL
Total water vs beverages — where food fits
“8 glasses a day” is a myth
The real check: thirst + urine colour
How we calculate this
Reviewed by Reckonist Editorial · Last reviewed July 2026. Figures follow the methods and sources set out in our editorial standards.
Bodyweight method (~33 mL/kg) plus activity and climate adjustments; NASEM total-water context. General hydration guidance, not medical advice.
NASEM · bodyweight method
Pair it with your daily fuel in the Macro Calculator, or plan eating windows with the Intermittent Fasting Calculator.
The bodyweight method — about 33 mL per kilogram
Your daily water target starts from your body weight: roughly 33 mL per kilogram(the 30–35 mL/kg range), which is close to the “half your weight in pounds, in ounces” shortcut. That base is then adjusted for activity and climate. Every value carries its unit — mL, L and fl oz.
Base (bodyweight)
≈ 33 mL/kg
base_mL = weight_kg × 33
70 kg → 2,310 mL. Pounds convert to kilograms first (× 0.453592).
Activity
≈ 12 mL per exercise minute
activity_mL = exercise_min × 12
45 min → 540 mL to replace sweat (8–16 mL/min range).
- 1Base from weight: 70 × 33 = 2,310 mL.
- 2Add activity: 45 × 12 = 540 mL.
- 3Total (temperate): 2,310 + 540 = 2,850 mL ≈ 2.85 L (~96 fl oz).
Activity & climate — the parts most calculators skip
Most water calculators stop at the bodyweight number. Two adjustments make the estimate personal: activity (about 8–16 mL of water per exercise minute to replace sweat) and climate(add roughly 10–20% in hot, humid conditions). This tool uses ≈ 12 mL/min and +15% for hot & humid.
Worked example · same profile, but hot & humid
“8 glasses a day” is a myth
The famous “drink 8 glasses a day” rule (eight 8-oz glasses ≈ 1.9 L) is not evidence-based. Hydration needs scale with body weight, activity and climate — there is no single number for everyone. A big, active person in the heat needs far more than 1.9 L; a small, sedentary person may need less.
Why the number varies
Total water vs beverage water — the NASEM numbers
NASEM (the US National Academies) put total daily water at about 3.7 L for men and 2.7 L for women — but those totals include the ~20% of water that comes from food. The bodyweight target here is beverage water (the drinks you pour), which is why it reads smaller. Subtract ~20% from a total-water figure to compare like with like.
Two framings, one need
The real check: urine colour & thirst
The number is a guide, not a quota. Day to day, the practical check is pale-straw-coloured urine and drinking to thirst — not hitting an exact millilitre target.
Don't over-drink
Frequently asked questions
The bodyweight method uses roughly 33 mL of water per kilogram (about 30–35 mL/kg), which is close to the "half your body weight in pounds, in ounces" shortcut. For a 70 kg (154 lb) person that is about 2,310 mL as a base, before adding water for exercise and hot weather. This tool estimates beverage water — the drinks you actually pour — and every value carries its unit (mL, L, fl oz).
No — the "8 glasses a day" rule is not evidence-based. Your water needs scale with your body weight, how much you exercise and the climate you are in, so there is no single number that fits everyone. Eight 8-oz glasses (about 1.9 L) is a rough average at best; a larger or very active person in a hot climate needs considerably more, and a small, sedentary person may need less.
Yes. NASEM (the US National Academies) put total daily water at roughly 3.7 L for men and 2.7 L for women, but those totals include the ~20% of water you get from food — fruit, vegetables, soups and so on. The bodyweight target this tool shows is beverage water only, which is why it looks smaller than the NASEM totals. The "from food" breakdown makes the two framings line up.
For activity, add roughly 8–16 mL of water per minute of exercise to replace sweat — this tool uses about 12 mL/min, so 45 minutes adds around 540 mL. For a hot, humid climate, add about 10–20% on top of your base-plus-activity total; this tool uses +15%. Both are general estimates — your real sweat rate depends on intensity, heat, humidity and your own physiology.
Yes. Forcing far more water than thirst dictates can dilute blood sodium and cause hyponatremia, which is dangerous. The practical day-to-day check is not hitting an exact millilitre target but aiming for pale-straw-coloured urine and drinking to thirst. Treat the calculated number as a guide, not a quota, and do not over-drink. This is general hydration guidance, not medical advice.
There is no separate "weight-loss" water requirement — the same bodyweight + activity + climate target applies. Drinking a glass of water before meals can modestly support appetite control, and staying hydrated helps you feel and perform better while dieting, but water is not a fat-burner. Use your bodyweight target as the baseline and drink to thirst.
Methods, formulas & references
Methodology: base = weight_kg × 33 (30–35 mL/kg); activity = exercise_min × 12 (8–16 mL/min); climate = (base + activity) × 15% in hot/humid conditions; total = base + activity + climate. Units: 1 fl oz = 29.5735 mL; 1 L = 1000 mL. Beverage-only = total × (1 − 20%), since NASEM total-water includes ~20% from food. All calculations run client-side and nothing is stored. General hydration guidance, not medical advice.
Cross-links
How we calculate this
Reviewed by Reckonist Editorial · Last reviewed July 2026. Figures follow the methods and sources set out in our editorial standards.
Daily water from the bodyweight method (~33 mL/kg) plus activity and climate adjustments, with NASEM total-water context (~20% of water comes from food). General hydration guidance, not medical advice.
Keep going
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