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Water Intake Calculator

Enter body weight and daily exercise minutes to get a daily water intake range and cup counts.

Eight glasses a day has been repeated for decades, but glasses differ in size and people in build, so the saying conveys almost nothing. The more practical calculation starts from body weight and adds the part lost to exercise, producing a daily range that belongs to you, converted into the usual cup counts — with notes below on whether soup and porridge count and who should not follow it.

On the convention: the intake here means plain water and unsweetened liquids; the water in soup, porridge and fruit is not counted and need not be deliberately replaced. Drinking a large volume at once — more than a litre in half an hour — loads the kidneys rather than helping, so smaller amounts more often is better. Anyone with impaired heart or kidney function needs a medically restricted intake instead.

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How to use

  1. Enter body weight and daily exercise minutes.
  2. Read the daily water range.
  3. Check the cup equivalent.
  4. Spread it through the day rather than drinking it all at once.

How it works

Conventions for daily water intake

Baseline intake is estimated by weight: 30-40 mL per kg. A 65 kg person maps to 1,950-2,600 mL (about 8-10 cups at 250 mL each). Heavier people need more, a more reasonable starting point than "8 cups a day" — 8 cups (2,000 mL) is just a memorable approximation.

How to replenish during exercise

Exercise compensation is 400 mL extra per 30 minutes: 45 minutes adds 600 mL, 60 minutes adds 800 mL. The principle is small sips often, not waiting for thirst; for high-intensity exercise over an hour, replenish with sodium electrolytes rather than plain water alone.

When not to follow this

More isn't better: patients with heart failure, kidney insufficiency or cirrhotic ascites need fluid restriction and must follow medical advice; drinking large amounts in a short time may also cause hyponatremia. Also, soup, congee, fruit, tea and coffee all count toward daily total water — you don't need plain water alone to fill the quota.

Calculation basis: baseline intake is estimated from the common guidance of 30–40 mL per kg of body weight, plus 400 mL per 30 minutes of exercise. Needs vary with climate, diet and health; people with kidney, heart or liver disease must follow their doctor's limit, and this is not medical advice.

Code example

JavaScript Baseline plus activity top-up 

function water(weightKg, sportMin) {
  const base = weightKg * 32.5;                    // 30~35mL/kg, the midpoint
  const sport = sportMin / 30 * 250;               // +250mL per 30 minutes
  return {
    base: Math.round(base),
    sport: Math.round(sport),
    total: Math.round(base + sport),
    cups: Math.round((base + sport) / 250)
  };
}

water(65, 60);   // total ≈ 2613mL ≈ 10 cups

Python The same formulas in Python 

def water(w, sport_min):
    base = w * 32.5
    sport = sport_min / 30 * 250
    return round(base + sport), round((base + sport) / 250)

water(65, 60)   # (2613, 10)

# Plain water only; soup, congee and fruit are not counted; small sips throughout the day

FAQ

Is 8 cups a day the standard?

It's just a memorable approximation (about 2,000 mL). A more reasonable approach is by weight: 65 kg is about 1,950-2,600 mL, more with higher weight, and more during exercise or hot weather.

Do tea, coffee and soup count as water intake?

They all count toward daily total water. Tea and coffee have a mild diuretic effect, but the net effect is still hydration (if not excessive); alcoholic drinks don't count, as alcohol increases water loss.

Can drinking too much be toxic?

Yes, but it takes large amounts in a short time (several liters within hours) to cause hyponatremia. Those who sweat heavily in a marathon or long intense exercise and replenish only plain water are at higher risk — use electrolyte drinks.

How should I replenish during exercise?

About 400 mL extra every 30 minutes, sipped in small amounts. For high-intensity exercise over an hour, or heavy sweating, choose a sodium-containing sports drink to help maintain electrolyte balance.

How do I know I've had enough?

Urine color is the most direct: pale yellow near clear means adequate, darker means it's time to replenish. Thirst actually appears when you're already mildly dehydrated, so don't treat it as the only reminder.

Who needs to restrict water intake?

Patients with heart failure, kidney insufficiency or cirrhotic ascites usually need fluid restriction, with the amount set by the doctor based on condition and lab results — don't follow this tool's range.

Is my weight data uploaded?

No. Weight and exercise duration are used only locally in the browser, not sent to a server or stored; the site has no account system linking to you. History stays in your browser and is clearable in one click.