Water Intake Calculator
Weight-based baseline plus an activity allowance. Includes the share that normally comes from food.
Total fluid per day
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From drinks
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In 250 ml cups
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Worked example
75 kg with 30 minutes of exercise needs about 2.8 litres of total fluid, of which roughly 2.2 litres should come from drinks — around nine 250 ml cups.
Water needs scale with body mass and losses, not with a fixed eight glasses. About a fifth of total intake normally comes from food, which is why the drinking figure is lower than the total.
Thirst is a reasonable guide
For healthy adults with free access to water, thirst tracks need closely. Fixed targets matter mainly for people whose thirst signal is unreliable — endurance athletes, older adults, and anyone in extreme heat.