How is the water intake calculated?

We start from roughly 35 ml of water per kilogram of body weight, add an allowance for activity, and apply a small multiplier for hot or humid climates. The result is shown in litres, US cups and fluid ounces.

Does food count towards the total?

Yes — food and other drinks contribute to your overall hydration, so you may not need to drink the full figure as plain water. Use it as a general daily target, not a strict rule.

Is my weight sent anywhere?

No. The calculation runs entirely in your browser and nothing is uploaded or stored.

Is 8 glasses of water a day right for everyone?

The "8 glasses" rule (about 2 litres) is a rough average, not a personalised figure. A 90 kg active person needs far more than a 55 kg sedentary one. Scaling by body weight, activity and climate gives a closer estimate for you.

How much extra water do I need when exercising?

This tool adds 350 ml for moderate activity and 700 ml for intense or long workouts on top of the weight-based baseline, then applies a hot-climate multiplier. Replace fluids lost to heavy sweating during the session as well.

Can you drink too much water?

Yes. Drinking far beyond your needs in a short time can dilute blood sodium (hyponatraemia), which is dangerous. Treat the figure as a daily target spread across the day, and let thirst and urine colour guide you.

Why does a hot climate increase the target?

Heat and humidity raise fluid loss through sweat and breathing, so the calculator multiplies the total by 1.1 (a 10% bump) for hot or humid conditions. In extreme heat or at altitude you may need more still.

Water Intake Calculator

Water intake calculator

How much water should you actually drink each day? The generic “8 glasses” rule ignores your size and lifestyle. This calculator estimates a personalised daily water target from your body weight, then adjusts for activity level and climate — useful for athletes, people in hot countries, or anyone wanting a number more grounded than a slogan.

How it works

The estimate starts from 35 ml of water per kilogram of body weight (imperial weight converts at 1 lb = 0.453592 kg). It then adds an activity allowance and applies a climate multiplier:

intake = (weight_kg × 35 + activity_ml) × climate_multiplier

Results are shown in litres, US cups (÷ 236.588 ml) and fluid ounces (÷ 29.5735 ml).

Adjustment	Value
Base	35 ml per kg
Low activity	+0 ml
Moderate activity	+350 ml
High activity	+700 ml
Temperate climate	× 1.0
Hot / humid climate	× 1.1

Example

A 70 kg person, moderately active, in a temperate climate:

(70 × 35 + 350) × 1.0 = (2,450 + 350) = 2,800 ml = 2.8 L (≈ 11.8 US cups · 94.7 fl oz)

Food and other drinks also contribute to hydration, so this is a daily target rather than a strict plain-water quota. Everything runs in your browser — nothing is uploaded.