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Water intake calculator: how much water to drink a day

  

35 ml per kg, plus 0.5 L per hour of exercise and 0.5 L on a hot day.

Units

kg
min

Hot or humid day?

Water a day

2.7 L

About 11 glasses of 250 ml, or 91 US fl oz.

Body weight × 35 ml
2.45 L
Exercise
0.25 L
Hot weather
0 L

How we got this

  1. 70 kg × 35 ml = 2.45 L
  2. 30 min ÷ 60 × 0.5 L = 0.25 L
  3. Total 2.7 L

Thirst is a good guide

For healthy adults, pale yellow urine is a simpler check than any formula. Use this number on hot days, long workouts or travel. People with kidney or heart conditions should follow their doctor's limit.

Training harder? Pair it with TDEE so food keeps up with the extra activity.

Sources

What this calculator does not account for

  • Water from food and other drinks, about a fifth of the total.
  • Kidney, heart or liver conditions that need a fluid limit.
  • Sweat rates, which vary a lot between people; drink to thirst.

How this is calculated

Formula: Weight-based water target

litres =kg × 0.035 + 0.5 × exercise hours + 0.5 (hot day)

What the symbols mean

  • kgBody weight in kilograms.
  • exercise hoursMinutes of exercise ÷ 60.

Good to know

  • One glass = 250 ml. 1 litre ≈ 33.8 US fl oz.
  • EFSA's reference for total water, drinks plus food, is 2.5 L for men and 2.0 L for women.

Read the full methodologyFound an error? Contact us

Worked examples

Each example is worked out by the same code as the calculator above.

70 kg, one hour of exercise

70 × 35 ml = 2.45 L, plus 0.5 L for the workout = 2.95 L, about 12 glasses.

55 kg, hot day, no exercise

55 × 35 ml = 1.925 L, plus 0.5 L for the heat = 2.425 L.

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Questions

Is 8 glasses a day right?

It is a rough rule. Two litres suits a 57 kg person by this formula; heavier or more active people need more.

Do tea, coffee and food count?

Yes. All drinks count, and food supplies around 20% of total water. Plain water is still the best default.

Can I drink too much?

Yes, rarely: several litres in a few hours can dilute blood sodium. Spread drinks through the day and drink to thirst.