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Water Intake Calculator: How Much to Drink

By Hesaplayıcı

The water intake calculator finds how much water an adult needs a day. Choose the values of the European Food Safety Authority (EFSA) or 35 ml per kg of body weight, and enter your exercise. It shows the total water including food, the part to drink and how many glasses that is. The result is not medical advice.

Adds 10 ml to drink for each minute.

Worked example: An adult woman

Water to drink

1.6 L

Total water a day (drinks and food)
2 L
Glasses (200 ml)
8 glasses
Step by step

  1. Total water a day (drinks and food)

    total water = EFSA (woman)

    total water = 2 L = 2 L

  2. Water to drink

    from drinks = total water × 80%

    from drinks = 2 × 80% = 1.6 L

  3. Glasses (200 ml)

    glasses = from drinks / 0.2 L

    glasses = 1.6 / 0.2 = 8

health.water-intake

How to use

  1. Choose the Method: EFSA values or By body weight.
  2. With EFSA values, choose For whom?: Adult woman, Adult man, Pregnant woman or Breastfeeding woman.
  3. With By body weight, choose your Units (Metric, Pounds or Stones) and enter your Weight.
  4. Enter your Exercise a day in minutes. Leave 0 if you do not exercise.
  5. Press Calculate. The result shows the total water a day, the water to drink and the number of glasses.

Formula

  • Exercise water = exercise minutes × 10 ml
  • Total water (EFSA) = EFSA adequate intake + exercise water
  • Total water (by weight) = weight (kg) × 35 ml + exercise water
  • Water to drink = (total water − exercise water) × 80% + exercise water
  • Glasses = water to drink / 0.2 L

Total water is the daily water from drinks and from food. EFSA’s adequate intakes are 2.0 L for women and 2.5 L for men, plus 0.3 L in pregnancy and about 0.7 L when breastfeeding. Adult values apply from 14 years. The body weight method takes 35 ml per kg, which gives 2.0 L at 57 kg and 2.5 L at 71 kg. With pounds or stones, the weight is converted to kg first (1 lb = 0.45359237 kg, 14 lb to a stone). The group applies to the EFSA method only.

Like the British Dietetic Association (BDA), the calculator assumes 80% of the water comes from drinks. Each minute of exercise adds 10 ml, 0.6 L an hour: the middle of the 0.4–0.8 L an hour that the American College of Sports Medicine (ACSM) gives as a start. You replace sweat by drinking, so all of the exercise water goes to the drinks. A glass is 200 ml.

Worked example

The worked example on this page shows an adult woman who does not exercise, with the EFSA method. The steps give EFSA’s total water value, the part to drink and the number of 200 ml glasses.

Limits

The values are for a moderate climate and moderate activity. Sweat rates differ a lot between people; hot weather can need more water. Rules per kg of body weight are rules of thumb with weak origins, a guide only (Vivanti, 2012). They can give too much with obesity. Use the EFSA method for pregnancy and breastfeeding. Children have other values. With kidney, heart and some other diseases your doctor sets the fluid amount.

Frequently Asked Questions

How many litres of water should I drink a day?

EFSA sets the total water need of an adult woman at 2.0 L a day and of a man at 2.5 L. Most of it comes from drinks; the BDA advises about 1.6 L of drinks for women and 2.0 L for men.

How many glasses of water a day?

With 200 ml glasses, about 8 for women and about 10 for men (BDA). Drinks other than water count too.

How is water intake calculated by body weight?

The body weight method takes 35 ml of total water per kg. That gives EFSA’s 2.0 L at 57 kg and 2.5 L at 71 kg. Rules per kg are rules of thumb and a guide only.

Do I need more water in pregnancy or when breastfeeding?

Yes. EFSA advises 300 ml more a day in pregnancy and about 700 ml more when breastfeeding. Use the EFSA method for pregnancy and breastfeeding.

How much more should I drink when I exercise?

The calculator adds 10 ml to the drinks for each minute of exercise, 0.6 L an hour. That is the middle of the 0.4–0.8 L an hour the American College of Sports Medicine (ACSM, 2007) gives as a start. Sweat rates differ a lot between people; hot weather can need more.

Calculation rules

  • The values are EFSA’s adequate intakes (EFSA Journal 2010;8(3):1459): 2.0 L of total water a day for women, 2.5 L for men; 300 ml more in pregnancy and about 700 ml more when breastfeeding. Adult values apply from 14 years.
  • Total water is the water from drinks and from food. Like the British Dietetic Association (BDA), the calculator assumes 80% comes from drinks; a glass is 200 ml.
  • The weight method takes 35 ml of total water per kg: that gives EFSA’s 2.0 L at 57 kg and 2.5 L at 71 kg. Rules per kg are rules of thumb with weak origins, a guide only (Vivanti, Eur J Clin Nutr 2012). They can give too much with obesity; for pregnancy and breastfeeding use the EFSA method.
  • The values are for a moderate climate and moderate activity. Each minute of exercise adds 10 ml (0.6 L an hour) to the drinks: the middle of the 0.4–0.8 L an hour that the American College of Sports Medicine (ACSM, 2007) gives as a start. Sweat rates differ a lot between people; hot weather can need more.
  • With pounds or stones the weight is converted to kg (1 lb = 0.45359237 kg). The result stays in litres and glasses of 200 ml.
  • With kidney, heart and some other diseases a doctor sets the fluid amount. The result is not medical advice.
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