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Daily Water Target by Weight Calculator

Enter your body weight and any activity bonus to estimate daily water.

How it is calculated

The target is a simple rule of thumb: water (mL) = weight (kg) × 33 + bonus (mL). Weight is in kilograms and must be above zero. The bonus is the extra millilitres you add for exercise, heat or other reasons; if it is empty, or negative, it counts as 0. The total is also shown in litres (mL ÷ 1000, two decimals) and in cups of 240 mL (mL ÷ 240, one decimal).

The tool does not decide the bonus for you, so you choose a figure that fits your day. It does not account for age, pregnancy, illness, medication, diet or climate, and the 33 mL per kg factor is a general estimate, not a medical recommendation. Part of daily fluid also comes from food and other drinks, so the number is a total fluid target rather than plain water only, and anyone told to limit fluids should follow their doctor's advice.

Worked example

A person weighs 70 kg and plans a workout that adds about 500 mL. Base amount: 70 × 33 = 2,310 mL. Add the bonus: 2,310 + 500 = 2,810 mL. In litres, 2,810 ÷ 1000 = 2.81 L. In 240 mL cups, 2,810 ÷ 240 = 11.7 cups. Without the bonus, a rest day would be 2,310 mL, or 2.31 L.

Try this example →

Common mistakes

  • Entering weight in pounds. The field is kilograms, so 154 lb typed as 154 would give 5,082 mL instead of the correct figure for about 70 kg.
  • Typing the bonus in litres. It is in millilitres, so a 0.5 litre extra must be entered as 500, not 0.5.
  • Entering a negative bonus to lower the target on a cool day. Negative values are ignored and counted as 0, so the base amount is not reduced.
  • Treating the total as plain water. Tea, soup and fruit also count towards fluid, so the figure does not mean you must drink that much from a glass.
  • Using the number when a doctor has set a fluid limit, for example with some heart or kidney conditions. A fixed medical limit always replaces a rule of thumb.

About this calculator

A common rule-of-thumb for hydration used across fitness and nutrition apps scales daily water intake to body size: roughly 33 mL of water per kilogram of body weight per day, which lands in the same general range as other commonly cited guidelines like “half your body weight in ounces.” Larger bodies have more metabolically active tissue and a greater fluid volume to maintain, so their baseline needs are higher.

Because that weight-based baseline does not account for how much you sweat, this calculator adds an optional activity bonus on top of it for exercise or hot-weather exertion. The result is a starting estimate for daily fluid intake, not individualized medical guidance — actual needs vary with climate, health conditions, and diet, so this is not a substitute for advice from a doctor or dietitian.

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  • Editorial team

    This is a total fluid target, not plain water, because food, tea and coffee also count. At 70 kg the rule gives 2,310 mL, about 2.31 L or 9.6 cups of 240 mL. The bonus box is yours to fill for exercise or heat, in millilitres, and it only adds to the base figure. Anyone on a fluid limit should follow their doctor. How much extra do you add on a training day?

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