Water Intake Calculator
Estimate daily fluid intake from your weight, activity and conditions, then compare it with general NHS-style hydration guidance.
Calculate your estimated daily fluid intake
Enter your body weight and activity level for a general daily hydration estimate. Follow medical advice over calculator results.
This includes water and other suitable drinks, not just plain water.
How this water intake calculator works
This calculator estimates daily hydration using your body weight, activity and conditions that can increase fluid loss. It is a planning tool, not a medical fluid prescription.
The NHS says most people should aim for 6 to 8 cups or glasses of fluid a day, but you may need more if you are pregnant or breastfeeding, in a hot environment, physically active for long periods, ill or recovering from illness.
Water intake formula
The calculator starts with a weight-based estimate, then adds a simple activity and heat adjustment.
Base fluid estimate = body weight in kg × 33ml
Minimum baseline = 1.2 litres
Activity addition = 500ml per 30 minutes of activity
Hot weather / heavy sweating addition = 500ml
Estimated daily fluid intake = base + additionsHow to interpret your result
Your result is an estimate of total fluid intake across the day. It can include water and other suitable drinks. Water is a healthy choice, but lower-fat milk and sugar-free drinks can also contribute.
Do not force yourself to hit an exact number. Fluid needs vary from day to day depending on heat, exercise, sweat, illness, food intake and medication. If you have a medical condition or have been given fluid instructions, use those instead.
Water intake examples
When not to rely on a water calculator
A water intake calculator can be useful for everyday planning, but it can be unsafe if your body needs are affected by health conditions, medication or illness.
- Follow professional advice if you have kidney, heart or fluid-balance issues.
- Get help if you have signs of dehydration after vomiting, diarrhoea, fever or heavy sweating.
- Pregnancy and breastfeeding can change fluid needs, so use this only as a broad guide.
- Older adults and young children can be more vulnerable to dehydration.
Water intake calculator FAQs
How much water should I drink per day?
There is no perfect number for everyone. NHS guidance says most people should aim for 6 to 8 cups or glasses of fluid a day, but needs vary with activity, heat, pregnancy, breastfeeding and illness.
Do tea and coffee count towards fluid intake?
Many drinks can contribute to your fluid intake. Water is a healthy choice, and lower-fat milk and sugar-free drinks can also count. Try to limit sugary drinks.
Can drinking too much water be a problem?
Yes, especially if you have certain medical conditions or drink extreme amounts in a short period. Do not force excessive fluid intake, and follow medical advice if you have been told to limit fluids.
Related glossary terms
Build a broader health estimate
Fluid intake is only one part of the picture. Estimate calories, protein and macros for a clearer planning view.
Results are estimates only and are not medical advice.