How much water should I drink a day?

A general guideline is to drink your body weight (in kg) multiplied by 33ml. For example, a 70kg person needs about 2.3 liters as a baseline. Activity level and climate can increase this by 15-60%.

Can you drink too much water?

Yes, drinking excessive water can lead to hyponatremia (low sodium levels), but this is rare and typically only occurs when drinking several liters quickly. For most people, spreading 3-4 liters throughout the day is safe.

Does coffee count as water intake?

Partially. Coffee provides about 80% of its volume in hydration due to its mild diuretic effect. A 250ml coffee contributes roughly 200ml to your daily water intake.

Water Intake Calculator

Calculate how much water you should drink daily based on your weight, activity level, and environment.

Your Weight

Unit

Activity Level

Climate / Environment

Caffeinated drinks per day (optional)

Coffee, tea, energy drinks

How Much Water Should You Drink Daily?

The general recommendation of “8 glasses a day” is a good starting point, but your actual needs depend on several factors including your body weight, activity level, and environment.

Water Intake by Weight Chart

Weight (lbs)	Weight (kg)	Sedentary	Active	Very Active
100	45	1.5L	1.9L	2.2L
140	64	2.1L	2.6L	3.1L
180	82	2.7L	3.4L	4.0L
220	100	3.3L	4.1L	4.9L

Signs You're Not Drinking Enough Water

Dark yellow urine (should be light yellow)
Feeling thirsty (you're already dehydrated)
Fatigue and low energy
Headaches
Dry skin and lips

Does Coffee Count Toward Water Intake?

Yes, but only partially. Coffee has a mild diuretic effect, meaning it causes you to lose some water. Studies suggest coffee provides about 80% of its volume in hydration. Our calculator accounts for this with a small adjustment for caffeine consumption.

Method & Scientific Basis

Daily target = body weight (kg) × 33 ml as a baseline, multiplied by an activity-level factor (1.0–1.6×) and a climate factor (1.0–1.3×), with an additional 80 ml per caffeinated drink to compensate for mild diuresis. The 33 ml/kg baseline is the conventional clinical heuristic; the activity and climate adjustments follow EFSA and Institute of Medicine guidance.

References

Institute of Medicine — Dietary Reference Intakes for Water (2004) — Source of the 2.7 L (women) / 3.7 L (men) total-water reference values that anchor the 33 ml/kg heuristic.
EFSA Panel — Scientific Opinion on Dietary Reference Values for Water (2010) — European reference for adult water requirements and climate adjustments.
Maughan & Griffin — Caffeine ingestion and fluid balance (J Hum Nutr Diet, 2003) — Basis for treating caffeinated drinks as ~80% hydrating, hence the +80 ml compensation per drink.