Health & Wellbeing2 min check

Water Intake Calculator

Estimate your daily fluid target — useful as a starting point for hydration, especially if active or in hot weather.

Short answer

NHS suggests 6–8 glasses (1.5–2 L) of fluid per day for most adults. EFSA gives a higher 'adequate intake' of 2.5L for men and 2L for women including all sources (food and drink). Add 0.5–1L per hour of vigorous exercise.

Step 1 of 10%

Calculation method, coverage and version

Inputs used: Body weight (kg), Vigorous exercise hours per day, Climate.
Calculation approach: The calculator applies the rules and assumptions described in “How it works” to the values you enter. Rounding can cause small differences from an official or provider calculation.
Coverage: Health & Wellbeing. UK nations, tax treatment, local rules and provider criteria can differ; check the official sources shown below before acting.
Content version: No page-specific review date is currently published. Treat the result as indicative and verify current rules independently.

Not included unless explicitly requested: personal circumstances not entered, provider discretion, future rule changes, professional fees and case-specific exceptions. Read the full calculator methodology.

How it works

A common rule of thumb is 30-35 ml per kg body weight. Add ~700 ml per hour of vigorous exercise. Multiply by ~1.2 in hot conditions.

Roughly 20% of fluid intake comes from food (fruits, vegetables, soups), so the drink target is the rest.

Worked example

70kg, 1 hour exercise, UK climate:

Baseline: 70 × 0.033 = 2.31 L
+ Exercise: 0.7 L
Total: ~3.0 L of fluid (about 12 glasses)

Who should use this

•Active adults setting a hydration target
•People recovering from illness or in hot weather
•Anyone tracking general wellness

Common mistakes

×Drinking only when thirsty (older adults especially have a blunted thirst signal)
×Forgetting that tea/coffee count — caffeine's diuretic effect is mild at habitual intakes
×Over-drinking — hyponatraemia is rare but possible at extreme intakes (>1 L/hr)
×Counting alcohol as hydration (it's net dehydrating)

Frequently asked questions

Does coffee dehydrate me?▾

Habitual caffeine consumers tolerate it without significant fluid loss. Coffee net contributes to hydration.

Can I drink too much water?▾

Yes — hyponatraemia (low sodium) can occur if you drink several litres very quickly, especially during endurance events.

Does food count?▾

Yes — fruits, vegetables, soups and stews can provide ~20% of daily fluid.

How can I tell if I'm hydrated?▾

Urine colour. Pale straw = good. Dark yellow = drink more. Clear constantly may mean over-drinking.

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