Water Intake Calculator

Calculate your recommended daily water intake based on weight, activity level and climate.

Last updated: April 2026 · Source: NHS — Water, drinks and hydration

Daily Water

3.0 litres

Millilitres

2,970 ml

Glasses (250ml)

12

Disclaimer

This calculator is provided for informational purposes only and should not be considered as financial or tax advice. All calculations are performed locally in your browser — no personal data is collected or sent to our servers. Rates and thresholds are sourced from HMRC and GOV.UK and are updated for the current tax year. Always verify results with HMRC or consult a qualified professional before making financial decisions.

How It Works

Daily water needs depend on body weight, activity level, climate and overall health. A common starting point is 30–35 ml per kilogram of body weight. The NHS recommends 6–8 glasses (approximately 1.2 litres) of fluid per day as a minimum, though active people and those in warm climates need considerably more.

This calculator uses your weight and activity level to estimate a personalised daily target in litres. Exercise adds roughly 500–1,000 ml per hour of moderate-to-vigorous activity. Hot or humid weather, illness with fever, and pregnancy or breastfeeding all increase requirements further.

All fluids count towards your total, including tea, coffee, milk and juice, as well as water from food (fruit, vegetables and soups contribute roughly 20% of daily intake). Caffeinated drinks do count, despite common myths — their mild diuretic effect is offset by the fluid they provide.

Example: 75 kg, moderately active (gym 3 times/week)

  1. Base intake: 75 × 35 ml = 2,625 ml
  2. Activity addition (3 sessions/week average): +350 ml/day
  3. Recommended daily intake: ~3.0 litres
  4. Equivalent to roughly 12–13 glasses (250 ml each)

Source: NHS — Water, drinks and hydration

Frequently Asked Questions

What does the Water Intake Calculator do?
Calculate your recommended daily water intake based on weight, activity level and climate. All calculations are performed in your browser using official UK rates and thresholds.
Is this medical advice?
No. This calculator is for informational purposes only and does not constitute medical advice. Always consult your GP or an appropriate healthcare professional for medical guidance.
Are the reference values from the NHS?
Where applicable, this calculator uses reference values and guidelines from the NHS and other UK health authorities. Individual needs may vary based on personal health circumstances.