Water Intake Calculator

Calculate your recommended daily water intake based on weight and activity.

Body weight

Unit

Activity level

Recommended daily intake

2695

Milliliters

2.69

Liters

Fluid oz

Glasses (250 mL)

Based on 35 mL/kg body weight adjusted for activity level. Individual needs vary — this is an estimate.

How much water should you drink per day?

A common recommendation is 35 mL per kg of body weight. Exercise, heat, and health conditions increase needs. The old "8 glasses a day" rule (1.9 L) is a rough average for a sedentary 65 kg person — it doesn't account for body size or activity. Thirst is a good guide: drink before you feel thirsty during exercise. Coffee and tea count toward hydration, though with minor diuretic effects. Related: BMI calculator and BMR calculator.

Built and maintained by Meet Shah · Last updated 19 July 2026

What this tool is used for

Getting a rough daily target from weight and activity.
Seeing how much a hot day or a workout adds.
Comparing your typical intake against an estimate.
Getting a figure to discuss with a professional.
Understanding roughly how much of intake comes from food.

Frequently Asked Questions

Where does the recommendation come from?: Body weight and activity level, which is the common rule-of-thumb approach — roughly 30–35 ml per kilogram, adjusted upward for exercise. It is a starting estimate, not a clinical prescription, and individual needs vary widely.
Is the eight-glasses rule real?: It has no clear scientific origin. It is often traced to a 1945 US recommendation of about 2.5 litres a day — which explicitly added that most of it comes from food. The memorable half got repeated and the qualifier did not.
Does coffee count?: Yes. Caffeine is a mild diuretic, but the fluid in the drink more than compensates, so tea and coffee contribute to hydration for habitual drinkers. Food contributes too — around a fifth of typical intake, more if you eat a lot of fruit and vegetables.
Can you drink too much water?: Yes, and it is dangerous. Drinking far more than the kidneys can excrete — roughly a litre an hour — dilutes blood sodium and causes hyponatremia, which has killed endurance athletes and hazing victims. More is not automatically better.
What is the simplest way to check?: Urine colour. Pale straw suggests you are well hydrated; dark amber suggests you are not. It responds within hours and needs no arithmetic — vitamin supplements can turn it bright yellow, which is harmless and not dehydration.
Does food and other drink count toward the total?: Yes — food supplies roughly a fifth of daily intake, and tea, coffee and juice all count despite the persistent belief that caffeine is a net loss. The figure here is total water, not extra water on top of everything.

Common errors and gotchas

Treating a formula as a requirement, when needs vary substantially by person and conditions.
Ignoring water from food and other drinks, which is a meaningful share of intake.
Assuming more is always better, when very high intake carries its own risks.
Using it as medical advice, particularly with a condition affecting fluid balance.
Recalculating daily and reacting to noise rather than to a trend.