Does this include water from food?

No. The figure is for drinking water only. Food typically provides an extra 20–30% of your daily fluid intake on top of what you drink.

Why does activity level matter so much?

You lose water through sweat, breathing, and metabolism — all of which increase with activity. Hard exercise can easily add 0.5–1 litre of fluid loss per hour.

Should I drink more on hot days?

Yes. Heat and humidity increase sweat rate significantly. This calculator gives a baseline; adjust upward in hot weather or when you are ill.

Are the glass and cup sizes standard?

The calculator uses 250 mL for a glass and 240 mL for a US cup. Your actual glasses or cups may differ — use the litre figure as the definitive target.

Can I use pounds instead of kilograms?

Yes. Select Imperial in the unit dropdown and enter your weight in pounds. The calculator converts to kg internally.

Daily Water Intake Calculator

Enter your body weight and activity level. The calculator estimates your recommended daily water intake in litres, fluid ounces, and the equivalent number of glasses.

Use it to get a personalised daily hydration target adjusted for your size and how active you are — then check the glass count to set a practical drinking goal.

Daily water intake

3.19 L

In fluid ounces: 107.7 fl oz
Glasses (250 ml): 13
Cups (240 ml): 13

The result updates as you change inputs. The primary figure is in litres; fluid ounces and glass/cup equivalents are shown beneath for easy reference.

How does it work?

This is a general guideline based on the 35 mL/kg rule. Individual needs vary with climate, health conditions, and diet. Water from food counts toward total hydration. Imperial weights are converted to kg internally.

Daily water intake formula

W = m \times 0.035 \times f_a

W: Daily water intake in litres.
m: Body weight in kilograms.
0.035: Base hydration factor: 35 mL per kg of body weight.
f_a: Activity multiplier: 1.0 (sedentary), 1.15 (lightly active), 1.3 (moderately active), 1.5 (very active), 1.7 (extra active).

A 70 kg person who is moderately active needs about 70 × 0.035 × 1.3 ≈ 3.19 litres per day.

Method & sources

The base guideline is 35 mL per kg of body weight, a commonly cited general recommendation. Activity multipliers (1.0–1.7) add extra water to account for fluid lost through exercise and physical labour. Imperial pounds are converted to kilograms (1 lb = 0.453592 kg) before the calculation.

Sources

Where this method comes from — use these references to understand the formula, assumptions, and limits.

Water, drinks and hydration — World Health Organization, verified 2026-06-10
Water, drinks and your health — NHS — NHS (UK National Health Service), verified 2026-06-10

How we calculate

The base guideline is 35 mL per kg of body weight, a commonly cited general recommendation.
Activity multipliers (1.0–1.7) add extra water to account for fluid lost through exercise and physical labour.
Imperial pounds are converted to kilograms (1 lb = 0.453592 kg) before the calculation.
One glass is defined as 250 mL; one US cup as 240 mL.
Water from food and other beverages is not included; this figure represents drinking water.
Individual needs vary with climate, health conditions, pregnancy, and breastfeeding — consult a healthcare professional for personal guidance.

Rounding

Litres are shown to two decimal places. Fluid ounces are shown to one decimal place. Glasses and cups are rounded to the nearest whole number.

What the calculator does

It multiplies your body weight in kilograms by 35 mL — a widely cited baseline — then applies an activity multiplier that accounts for the extra fluid you lose through exercise and physical work. The result is converted to litres, fluid ounces, and glass equivalents.

How to use it

Choose your weight unit (kg or lbs).
Enter your body weight.
Select your activity level from the dropdown.
Read your recommended daily intake in litres, fluid ounces, and glasses.

Understanding the activity levels

Sedentary: desk job, little or no planned exercise.
Lightly active: light exercise 1–2 days a week.
Moderately active: moderate exercise 3–5 days a week.
Very active: hard exercise or sport 6–7 days a week.
Extra active: very hard physical job or twice-daily training.

An example

A moderately active person weighing 70 kg needs about 70 × 0.035 × 1.3 ≈ 3.19 litres per day — roughly 13 glasses of 250 mL each. In a sedentary day, the same person needs about 2.45 litres (10 glasses).

When it is useful

Setting a daily drinking goal, adjusting intake on training days versus rest days, or checking whether you are likely meeting minimum hydration guidelines.

FAQ

Does this include water from food?: No. The figure is for drinking water only. Food typically provides an extra 20–30% of your daily fluid intake on top of what you drink.
Why does activity level matter so much?: You lose water through sweat, breathing, and metabolism — all of which increase with activity. Hard exercise can easily add 0.5–1 litre of fluid loss per hour.
Should I drink more on hot days?: Yes. Heat and humidity increase sweat rate significantly. This calculator gives a baseline; adjust upward in hot weather or when you are ill.
Are the glass and cup sizes standard?: The calculator uses 250 mL for a glass and 240 mL for a US cup. Your actual glasses or cups may differ — use the litre figure as the definitive target.
Can I use pounds instead of kilograms?: Yes. Select Imperial in the unit dropdown and enter your weight in pounds. The calculator converts to kg internally.

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