Does coffee count towards my intake?

Yes. The mild diuretic effect of normal coffee and tea consumption is smaller than the fluid volume they provide, so they contribute net positively.

Is the '8 glasses a day' rule right?

It is a rough average, roughly 2 litres, that ignores body size, activity and climate. A weight-based estimate is a better starting point.

Can you drink too much water?

Yes — drinking litres in a short period can dilute blood sodium, a dangerous condition called hyponatraemia. Spread intake through the day.

Water Intake Calculator

Fluid needs scale with body size, how much you sweat and how warm your environment is. This calculator starts from a weight-based baseline and adds allowances for training and heat.

Fill in the fields above and select Calculate to see your result and the full working.

Please note: Health calculators on this site provide general estimates based on population-level formulas. They are not medical advice and cannot account for your individual medical history. Speak to a qualified healthcare professional before making decisions about diet, medication or training.

Formula used

Litres per day ≈ 0.033 × body weight (kg) + 0.35 L per 30 minutes of exercise + climate allowance

How to use this calculator

Enter your body weight in kilograms or pounds.
Add the average number of minutes you exercise each day.
Choose the climate you spend most of the day in.
Spread the resulting total across the day rather than drinking it in a few large servings.

Example calculation

A 70 kg person doing 45 minutes of exercise in a warm climate:

Baseline = 70 × 0.033 = 2.31 L

Exercise = 45 ÷ 30 × 0.35 = 0.53 L

Warm climate = +0.35 L → about 3.2 L a day.

What does this result mean?

The target counts all fluids, including tea, coffee, milk and the water in food. Pale straw-coloured urine and the absence of thirst are the practical signs you are hydrated. Needs rise with fever, breastfeeding, altitude and some medications, and certain heart and kidney conditions require a restricted intake — follow your clinician's advice over any calculator.

Frequently asked questions

Does coffee count towards my intake?: Yes. The mild diuretic effect of normal coffee and tea consumption is smaller than the fluid volume they provide, so they contribute net positively.
Is the '8 glasses a day' rule right?: It is a rough average, roughly 2 litres, that ignores body size, activity and climate. A weight-based estimate is a better starting point.
Can you drink too much water?: Yes — drinking litres in a short period can dilute blood sodium, a dangerous condition called hyponatraemia. Spread intake through the day.

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