CalcPenguin

Water Intake Calculator

Estimate how much water to drink each day from your weight, how much you exercise, and whether you live somewhere hot.

Your numbers are saved in this browser.
kg
minutes

Water a day

3.2 litres

In 250 ml glasses
13 glasses

Aim for about 3.2 litres of fluid a day, roughly 13 glasses. Pale yellow urine is a good sign you're drinking enough.

How it's worked out

  1. Base need70 kg × 33 ml2.31 L
  2. Exercise30 min ÷ 30 × 350 ml0.35 L
  3. Heat0.5 L
  4. Total3.16 L
  • A general guide. Food provides about a fifth of daily water. People with kidney or heart conditions should follow their doctor's advice.

How the estimate works

Water = 33 ml × weight + 350 ml per 30 minutes of exercise + 500 ml in hot weather

Worked example

A 70 kg person who exercises 30 minutes a day in a hot climate needs about 2.31 + 0.35 + 0.5 = 3.2 litres a day, roughly 13 glasses.

Questions people ask

How much water should I drink a day?

A common guide is about 33 ml per kg of body weight, plus more for exercise and heat. For 70 kg that's about 2.3 litres before exercise.

Does tea or coffee count?

Yes, most drinks count towards fluid. Food also provides about a fifth of your daily water.

How do I know I'm drinking enough?

Pale yellow urine and rarely feeling thirsty are good signs. Dark urine or headaches can mean you need more.

Formula and rules last checked 25 October 2026Written and tested by the CalcPenguin teamReport a problem