Quick answer
That is a general guide, not a personal prescription. You may need more if you are active, pregnant or breastfeeding, in hot weather, ill, recovering from illness or sweating heavily.
Hydration is not just about plain water. Water is a good choice, but lower-fat milk, sugar-free drinks, tea and coffee can also count towards your daily fluid intake.
Estimate your daily fluid target
Use weight, activity and hot-weather adjustments to get a simple hydration estimate.
UK guidance: 6 to 8 cups is a starting point
The NHS says the government recommends aiming for 6 to 8 cups or glasses of fluid a day. It also says most people should drink enough during the day so their pee is a clear pale yellow colour.
This is why a single “drink exactly this many litres” answer is too simplistic. A small person sitting indoors on a cool day may need less than someone doing physical work in hot weather.
| Simple benchmark | What it means | Important caveat |
|---|---|---|
| 6 to 8 cups/glasses | A broad UK public-health guide for daily fluid intake. | Needs vary by activity, weather, pregnancy, breastfeeding and illness. |
| Pale yellow pee | A practical sign many people use to check they are drinking enough. | Some medicines, vitamins and health conditions can affect urine colour. |
| Calculator estimate | A planning number based on body weight and activity. | It should not override medical advice or fluid restrictions. |
What counts towards fluid intake?
Fluid intake does not have to mean only plain water. The NHS lists water, lower-fat milk and sugar-free drinks, including tea and coffee, as drinks that can count.
- Water: usually the simplest choice because it has no sugar or calories.
- Lower-fat milk: contributes fluid and nutrients such as calcium.
- Tea and coffee: can count, although caffeine may not suit everyone.
- Sugar-free drinks: can contribute fluid, but water is still the easiest everyday option.
- Food: some fluid also comes from foods, especially fruit, vegetables, soups and stews.
When might you need more fluid?
Your fluid needs are not fixed. You may need more than the basic guide if your body is losing more fluid or your daily routine changes.
If you have kidney, heart or liver conditions, or you have been told to restrict fluids, follow professional advice rather than a generic online estimate.
How a water intake calculator estimates your target
A simple calculator can use body weight as a starting point, then add extra fluid for activity or hot conditions. This is only a planning method, not official NHS dosing.
Base estimate = body weight in kg × 33ml
Activity addition = about 500ml per 30 minutes of exercise
Hot weather addition = about 500ml
Daily estimate = base estimate + adjustmentsFor example, someone weighing 70kg would get a base estimate of about 2.3 litres before extra activity or heat adjustments. That does not mean everyone at 70kg must drink exactly 2.3 litres every day.
Calculate your estimate
Use the calculator to compare a weight-based estimate with the general 6 to 8 glasses guide.
Worked examples
These are planning examples, not medical targets.
| Scenario | Inputs | Rough estimate | What to remember |
|---|---|---|---|
| Office day | 70kg, no exercise | About 2.3 litres | Spread drinks through the day rather than forcing a large amount at once. |
| Gym day | 80kg, 60 minutes exercise | About 3.6 litres | Sweat rate varies; thirst, urine colour and how you feel still matter. |
| Hot day | 60kg, 30 minutes exercise, hot weather | About 3.0 litres | Heat can increase needs, but medical fluid restrictions still take priority. |
Signs you may not be drinking enough
Dehydration can happen when you lose more fluid than you take in. NHS guidance says you should drink fluids if you have symptoms of dehydration, starting with small sips if you feel sick.
- Feeling thirsty
- Dark yellow or strong-smelling pee
- Peeing less often than usual
- Feeling dizzy, lightheaded or tired
- Dry mouth, lips or tongue
These signs are not a diagnosis. If symptoms are severe, persistent or linked to illness, get medical advice.
Can you drink too much water?
Yes, although most everyday hydration problems are about drinking too little rather than too much. Drinking extreme amounts of water can be dangerous, especially during endurance events or if it dilutes blood sodium levels.
Do not force water far beyond thirst, comfort or medical advice. If you are exercising for a long time, sweating heavily or feeling unwell, hydration may involve salts and food as well as fluid.
Common mistakes
- Thinking only plain water counts: Water is best for many people, but other suitable drinks and some foods contribute fluid too.
- Copying someone else's litres: Body size, activity and heat change the number.
- Ignoring illness: Fever, vomiting or diarrhoea can increase fluid loss.
- Waiting until bedtime: Cramming drinks late in the evening can disturb sleep.
- Overriding medical advice: Some people need specific fluid limits or targets.
When to get medical help
Get medical advice if dehydration symptoms are severe, you cannot keep fluids down, you have ongoing diarrhoea or vomiting, or you are worried about a baby, child, older adult or someone with a long-term condition.
If you have been told to limit fluids because of a health condition, do not use a water calculator to increase your intake without checking with a qualified professional.
Sources used
This guide uses public information from the NHS water, drinks and hydration guidance, NHS dehydration guidance, the British Dietetic Association fluid and hydration guide, and the British Nutrition Foundation hydration information. It is general information only and does not replace advice from a GP, dietitian, midwife or other qualified professional.
FAQs
How much water should I drink per day?
For most people, UK guidance is to aim for around 6 to 8 cups or glasses of fluid a day. Some people need more depending on activity, heat, pregnancy, breastfeeding or illness.
Does tea or coffee count as water intake?
Tea and coffee can count towards fluid intake. Water is still a simple everyday choice, and people sensitive to caffeine may need to limit caffeinated drinks.
Is 2 litres of water a day right for everyone?
No. Two litres can be a useful rough number for some adults, but needs vary. A smaller, inactive person may need less; an active person in hot weather may need more.
What colour should my pee be?
NHS guidance says most people should drink enough during the day so their pee is a clear pale yellow colour. Dark yellow pee can be a sign that you may need more fluid.
Should I drink more water to lose weight?
Water can help replace sugary drinks and support general habits, but it is not a weight-loss treatment by itself. If weight management is your goal, look at overall diet, activity, sleep and sustainable calorie balance.