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Water Intake Calculator

Water intake is estimated from body weight: the common guideline is 35 millilitres for every kilogram you weigh, which is 2450 mL at 70 kg. The number is a starting point rather than a rule, because food, other drinks, heat and exercise all shift it.

Total daily fluid

2,450

The same total in litres
2.45
The same total in eight-ounce cups
10.3555
The same total in US fluid ounces
82.8444

Values update as you type. This calculator covers the single scenario its formula assumes — see Common Mistakes for what it leaves out.

The formula this calculator uses

mL = bodyweight (kg) x mL per kg

w
Body weight in kilograms
r
Millilitres per kilogram — 35 mL/kg/day is the usual adult guideline
V
Total daily fluid, equal to w x r
cups
The same total expressed in eight-ounce cups, 236.5882365 mL each

How to check the result by hand

  1. 1

    Convert your weight to kilograms

    The coefficient is written for kilograms, so convert before doing anything else: one pound is 0.453592 kilograms. A 154-pound adult is about 70 kg, which is the figure the rest of the calculation expects.

  2. 2

    Multiply by millilitres per kilogram

    Use 35 mL/kg as the standard adult guideline, or 30 to 40 to reflect activity and climate. For 70 kg the product is 70 x 35 = 2450 mL, the total fluid for a full day.

  3. 3

    Subtract what food and other drinks already provide

    Food and drinks other than plain water cover a substantial part of the 2450 mL, so the drinking target is lower than the total. Counting the whole figure as a water quota double-counts fluid you already consume.

  4. 4

    Convert to litres and cups

    2450 mL is 2.45 litres, 10.355544452439418 eight-ounce cups and 82.84435561951534 US fluid ounces. One eight-ounce cup is 236.5882365 mL and one US fluid ounce is 29.5735295625 mL.

  5. 5

    Adjust for heat, exercise and altitude, and stop short of excess

    Add 500 to 1000 mL on hot days, roughly 400 to 800 mL per hour of exercise, and more at altitude. Do not force large volumes: drinking far beyond losses can dilute blood sodium, so thirst is a useful guide.

For worked examples, common mistakes and the limits of this formula, read the full How To Calculate Water Intake page.