Water Intake Calculator

United Kingdom rules and figures

• The NHS says to aim for 6 to 8 cups or glasses of fluid a day, and to drink more in hot weather, during illness or when exercising.
• The NHS gives no litre figure, so this page does not claim one as official. Its starting goal of 2,500 ml is the tool's own number.
• Weight starts in stones and pounds on the UK page, with 11 st 0 lb as the sample, while volumes are shown in millilitres.
• The NHS advice covers fluid in general, which is why the drink list includes tea and coffee beside water, each counted by its own hydration value.

Sources: NHS: Water, drinks and hydration (checked 2026-11-08)

How the water intake calculator works

The recommended target starts at 35 mL per kilogram and is scaled by activity, climate and the other settings, then limited to 50 mL per kilogram. Drinks you log are weighted by a hydration value and compared with your daily goal, which starts at 2,500 ml because the NHS gives no litre figure.

69.85 kg × 35 = 2,445 mL; × 1.25 (Moderate) × 1.0 (Temperate) = 3,056 mL; ceiling = 69.85 × 50 = 3,493 mL

• Weight is entered in stones and pounds on the UK page and converted to kilograms, so 11 st 0 lb is used as 69.85 kg.
• Activity multiplies the base by 1.0 to 1.6, climate by 0.9 to 1.4, and choosing male adds 5%. Older and younger ages, altitude above 2,500 m, pregnancy, breastfeeding and fever add or take away smaller amounts.
• Water and sparkling water count fully, herbal tea 0.95, coconut water 0.95, green tea 0.9, sports drink 0.9, fruit juice 0.85, coffee 0.8, soda 0.6 and an alcoholic drink 0.3.
• Because no national litre figure exists, the Daily Water Goal starts at the tool's own 2,500 ml, and a goal you type is kept.
• Volumes are in ml, and logs are stored in ml whichever unit is on screen.

How to use the water intake calculator

1. Describe yourself. Open Settings and enter weight in stones and pounds, with an optional age, height and gender. Weight can be switched to kilograms.
2. Say how active and how warm. Choose an activity level and a climate. Both change the figure far more than altitude or the three health boxes do.
3. Log a drink. Choose a drink, type the amount in ml or use a quick-add button, then add it to today's list.
4. Read the four figures. Analysis lists the minimum, recommended, optimal and maximum safe amounts and every factor behind them.
5. Set a goal or take the data. On Goals, Use recommended copies the calculated target into your daily goal. Share Report copies a summary, and Export Data downloads everything as JSON.

Example: An adult at 11 st 0 lb, Moderate activity, Temperate climate

At 69.85 kg the Minimum is 2,096 ml, the Recommended target 3,056 ml, Optimal 3,362 ml and Max Safe 3,493 ml. The goal begins at 2,500 ml. Logging 250 ml water, 250 ml coffee and 500 ml sports drink adds 1,000 ml, but hydration values make it 250 + 200 + 450 = 900 ml, which is 36% of the 2,500 ml goal.

When something else is a better fit

• When you want a daily check-off with real streaks and history, use the Habit Tracker.
• When you want calories and macro targets for the same profile, use the Calorie Calculator.
• When you have a medical condition that affects fluids, use your clinician's guidance, which overrides any general formula.

Questions about the water intake calculator