Does coffee or tea count?

Yes — both contribute meaningfully to your daily fluid intake. The classic claim that caffeine "dehydrates" you was overstated by older studies and is no longer supported.

Can you drink too much water?

Yes — hyponatraemia (low blood sodium) can occur if huge volumes are consumed quickly without enough electrolytes. Stick close to your target and don’t force-drink.

Should I drink more on a hot day?

Yes. Hot or humid weather can increase fluid needs by 10–20% even without exercise.

Is mineral water better than tap water?

For hydration, no — water is water. Minerals are nice-to-have, not necessary, and most of the body’s mineral intake comes from food.

How can I drink more easily?

Carry a 500–750 ml bottle, drink a full glass with each meal, and set 2–3 light reminders during the day. It quickly becomes automatic.

Hydration · Daily intake

Water Intake Calculator

Personal hydration target based on body and activity.

Your details

Weight

Daily exerciseVigorous activity

hours

Climate

Counts all fluid sources — water, tea, coffee, soup, and water from food (about 20% of intake).

Daily target

2.6L / day

From food + drinks combined.

250 ml glasses

US fluid ounces

Why hydration matters

Water powers every cell, every joint, every thought. Even mild dehydration (1–2% body-mass loss) reduces concentration, mood and exercise performance. Hydration isn’t a one-size-fits-all eight glasses — it depends on you.

How we calculate your target

We start at 35 ml per kg of body weight, add 500 ml per hour of vigorous exercise, and apply a 15% multiplier in hot or humid climates. The number you get covers all fluid intake — water, tea, coffee, broth and water from food.

Beyond “8 glasses a day”

The famous “8 × 8” rule has no rigorous scientific basis. A precise per-kg estimate is more honest and far more useful — especially for athletes, larger bodies, or people in warm climates.

Limitations & caveats

This is a daily target, not a prescription — sip steadily, don’t chug.
Heat exposure, fever, diarrhoea, breastfeeding and altitude all raise needs.
Some medications and conditions (e.g. kidney disease, heart failure) require restricted fluid intake — follow your clinician.
Caffeine and alcohol have mild diuretic effects but still contribute to daily intake.
Pale-yellow urine is a more reliable real-time signal than any calculator.
Children and infants have different per-kg needs and should use pediatric guidance.