Hydration Calculator

How much water should you drink a day?

There is no universal daily water number that fits every person and every day. Body weight can provide a practical starting range, but activity, sweat loss, temperature, humidity, meals and other drinks all affect the amount you may need. Use the calculator as a planning aid, then adjust when the day changes.

National reference values often describe total water, which includes food as well as drinks. That is why a reference figure and a plain-water target can look different. HydrateWise avoids treating every millilitre as extra water you must drink on top of tea, coffee, milk, soup, fruit and other moisture-rich foods. The UK daily water guide compares the calculator with general NHS guidance.

Go beyond a daily number

Measure a representative workout with the sweat-rate calculator, or turn your estimate into full containers and refill checkpoints with the bottle and refill planner. Clubs, coaches and wellbeing teams can also use the free website widget.

How the daily water estimate works

The estimate begins with a transparent weight-based range and adds broad adjustments for the activity level and climate you select. It returns litres, millilitres and cup equivalents so you can translate the result into the bottle or glass you actually use.

The number is deliberately an estimate, not a diagnosis of hydration status or a prescription. A cool rest day, a long workout and a humid travel day should not share one automatic target. Review the calculation methodology and use the hydration planner to turn the total into comfortable servings rather than trying to catch up quickly.

What counts towards fluid intake?

Water is a simple default, but it is not the only drink that contributes. Ordinary tea and coffee, milk, sparkling water and diluted drinks all provide fluid. Food also supplies water. Count a prepared drink once, consider caffeine and sugar separately, and avoid adding a complete beverage target on top of a total-water reference.

Use the drink hydration checker for an instant explanation of common drinks. Alcohol contains water but is not a hydration strategy, especially around heat, exercise or illness. Vomiting and diarrhoea can also require more than plain water; a pharmacist may recommend an oral rehydration solution with a specific balance of sugar and salts.

When your needs may increase

Exercise, hot or humid weather, fever, vomiting and diarrhoea can increase fluid loss. For sport, session length, intensity, clothing and personal sweat rate matter more than the label “active.” Water suits many shorter sessions, while prolonged heavy sweating may make electrolytes and an individual sweat-rate plan more relevant.

Kidney, heart and liver conditions, pregnancy and some medicines can change what is safe. Follow personal clinical guidance where it applies. Persistent excessive thirst, very frequent urination or recurring symptoms should be discussed with a qualified healthcare professional.

Signs you may need more fluid

Thirst, a dry mouth, headache, tiredness, darker urine and urinating less often can occur with dehydration, but none is a perfect test by itself. Consider the pattern and what has happened that day. Start with comfortable servings rather than forcing a large amount.

Confusion, difficulty waking, breathing difficulty, collapse or signs of shock need urgent medical help. Heat illness can overlap with dehydration and is not fixed simply by completing a water target. Read the full guide to dehydration signs and when to seek help.