How Much Water Should I Drink A Day Calculator NHS
This independent hydration calculator helps adults turn the UK Eatwell Guide recommendation of 6 to 8 cups or glasses of fluid a day into a simple daily range. It is a general guide, not a personalised medical prescription.
Daily Fluid Guide Calculator
The NHS says 6 to 8 cups or glasses is only a guide. Needs can be higher during pregnancy or breastfeeding, hot weather, prolonged physical activity, or illness/recovery.
What is this calculator?
The NHS and UK Eatwell Guide advise most people to aim for 6 to 8 cups or glasses of fluid a day. This tool converts that guidance into litres using the cup or glass size you enter. For example, six to eight 250 ml glasses equals about 1.5 to 2.0 litres.
What counts as fluid?
Water is a healthy choice, but lower-fat milk and sugar-free drinks, including tea and coffee, can also count. Some fluid also comes from food. Fruit juice and smoothies count towards fluid intake, but NHS guidance says to limit them to a combined 150 ml per day because of free sugars.
How to use it
- Enter the capacity of the cup or glass you normally use in millilitres.
- The calculator multiplies that size by 6 and by 8.
- Use the displayed range as a general UK hydration guide, not a fixed medical target.
Formula or methodology
Lower guide = cup size × 6. Upper guide = cup size × 8. The result is converted from millilitres to litres by dividing by 1,000.
Worked example
With a 250 ml glass: 250 × 6 = 1,500 ml (1.5 L) and 250 × 8 = 2,000 ml (2.0 L). This represents the Eatwell Guide range using that particular glass size.
When might you need more fluid?
The NHS notes that you may need more if you are pregnant or breastfeeding, in a hot environment, physically active for long periods, ill or recovering from illness. Most people can also use pale clear-yellow urine as a practical hydration guide.
Important limitations
This tool does not use body weight to invent a personalised water prescription because the NHS public guidance is framed as a general 6-to-8-cup guide rather than one universal ml-per-kg formula. People with medical conditions or prescribed fluid restrictions should follow advice from their healthcare team rather than this calculator.
Authoritative sources
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FAQs
How much water should I drink a day according to the NHS?
The NHS says most people should aim for 6 to 8 cups or glasses of fluid a day, while recognising that individual needs can vary.
Do tea and coffee count towards fluid intake?
Yes. NHS guidance says tea and coffee can count towards daily fluid intake.
Do I need more water when exercising or in hot weather?
You may need more fluid if you are physically active for long periods or in a hot environment.
Is 2 litres of water mandatory every day?
No. The 6-to-8-glass recommendation is a guide, and the volume depends partly on glass size and individual circumstances.
Disclaimer: This independent calculator provides general hydration information only. If a clinician has advised you to restrict or change your fluid intake, follow that advice.