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Daily water intake calculator

Estimate a general daily water intake range from body weight and exercise duration, using commonly cited reference formulas.

General reference range
2.8 L per day
Baseline (35 mL per kg)2.45 L
Addition for exercise0.35 L
In cups (approx. 240 mL each)11.67
In standard 500 mL bottles5.6

A general population reference, not a personalised medical recommendation. Actual needs vary substantially with climate, altitude, health conditions, pregnancy and diet — food itself typically supplies 20% or more of total water intake, which this estimate does not separately account for.

This calculator applies a commonly cited general reference — roughly 35 millilitres per kilogram of body weight per day — with an addition for exercise duration, to give a rough daily water intake range. It is a starting point for a very individual question, not a precise personal prescription.

Baseline ≈ 35 mL × body weight (kg), plus roughly 350 mL per 30 minutes of exercise

Why there is no single correct number

Total water needs depend on far more than body weight: climate and humidity, altitude, activity level, diet composition, and individual physiology all shift the real requirement, sometimes substantially. Someone in a hot, humid climate doing physical labour outdoors needs considerably more water than the same body weight sitting in an air-conditioned office — a gap this simple formula cannot capture, since it only takes weight and exercise duration as input.

Food already supplies a meaningful share

A commonly cited estimate is that roughly 20% of daily water intake in a typical diet comes from food itself — fruits and vegetables in particular are largely water by weight. This calculator estimates total fluid need generally, without separately breaking out how much should come from drinking versus food, since that split depends heavily on individual diet.

Thirst is a reasonably good guide for most healthy people

For most healthy adults under normal conditions, thirst is a reasonably reliable physiological signal for hydration needs — the body has a functioning regulatory system for this. Formula-based estimates like this one are more useful as a rough sanity check or as a planning aid (how much water to carry on a hike, say) than as a strict target to hit exactly every day.

When to seek more specific guidance

Certain conditions change fluid needs significantly and are outside the scope of any general formula — kidney disease, heart failure, pregnancy, certain medications, and endurance exercise in heat all shift the picture in ways that deserve individualised medical guidance rather than a generic calculation. If you have a relevant health condition, or unusual thirst, urination or fluid retention patterns, that is a conversation for a doctor, not a formula.

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