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Water Intake Calculator

Get a daily water target from your body weight and how long you exercise. The calculator uses the common rule of half your body weight in pounds as fluid ounces, then adds an allowance for each half hour of activity.

Quick examples
min
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Daily water target92 fl oz
8 oz glasses
11.5
From body weight
80 fl oz
Added for exercise
12 fl oz

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      Formula

      Base (fl oz) = body weight (lb) × 0.5 — about 33 mL per kg
      Exercise allowance = 12 fl oz (about 350 mL) for every 30 minutes
      Daily target = base + exercise allowance

      How to use it

      1. Enter your body weight in pounds or kilograms.
      2. Enter the minutes of exercise you do on a typical day.
      3. Read your target in fluid ounces, liters or cups, and as a count of 8 oz glasses.

      Worked examples

      A 160 lb adult who exercises 30 minutes a day (80 + 12 = 92 fl oz)

      Daily water target
      92 fl oz
      From body weight
      80 fl oz
      8 oz glasses
      11.5

      A 70 kg adult on a rest day (about 77 fl oz)

      Daily water target
      77.2 fl oz
      8 oz glasses
      9.6

      How to use the number

      There is no single scientifically fixed water requirement; this is a rule of thumb. For reference, the US National Academies set an adequate intake of total water — from all drinks and food — of about 3.7 liters a day for men and 2.7 liters for women. Around a fifth of that typically comes from food.

      Needs rise in hot weather, at altitude, during pregnancy and breastfeeding, and with illness. Tea, coffee, milk and other drinks count toward the total. Pale yellow urine and rarely feeling thirsty are practical signs you are drinking enough.

      People with heart or kidney conditions are sometimes told to limit fluids. This is an estimate for general information, not medical advice. Talk to a doctor or other qualified clinician before making health decisions based on it.

      Questions people ask

      How much water should I drink a day?

      By the half-your-weight rule, a 160 lb adult would aim for about 80 fl oz (2.4 liters) a day, or 92 fl oz with 30 minutes of exercise — about eleven and a half 8 oz glasses.

      Is eight glasses a day enough?

      Eight 8 oz glasses is 64 fl oz (1.9 liters). That is a reasonable floor for many adults, though larger or more active people will usually want more.

      Does coffee count toward water intake?

      Yes. Caffeinated drinks have a mild diuretic effect but still add more fluid than they cause you to lose.

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