Water Intake Calculator

How much water do adults need?

The US National Academies set adequate intakes for total water, from all drinks and food, of about 3.7 liters a day for men and 2.7 liters for women. Roughly 20% usually comes from food, leaving about 3.0 and 2.2 liters from drinks.

Worked example

A man who exercises for 30 minutes a day: 3.7 × 0.8 = 2.96 L from drinks, plus about 0.35 L for exercise, is roughly 3.3 liters (112 fl oz).

Signs you are well hydrated

• Pale yellow urine.
• Rarely feeling thirsty.
• No headaches or dizziness from heat or exercise.

If you have kidney, heart or liver conditions, or a doctor has advised a fluid limit, follow their guidance instead.

Frequently asked questions

Do I really need 8 glasses a day?

The 8 × 8 rule is a simple rule of thumb. Needs vary with body size, activity and climate.

Do coffee and tea count?

Yes. Caffeinated drinks still add to your daily fluid intake.

Can you drink too much water?

Yes. Drinking very large amounts quickly can dangerously lower blood sodium.

How much extra water do I need when exercising?

A common guideline is about 12 fl oz (350 mL) for every 30 minutes, more in hot weather.