The Water Intake Calculator is a free tool that helps you calculate water intake using the formula Base = 35 ml x weight(kg) + activity adjustment. Enter your values above and press Calculate to get recommended water, glasses (250 ml) instantly, with a full step-by-step breakdown.
What is the Water Intake Calculator?
The water intake calculator is a free online tool that helps you calculate water intake quickly and accurately. It applies the standard formula Base = 35 ml x weight(kg) + activity adjustment to the values you enter and, when you press Calculate, displays the result together with a clear, step-by-step explanation of how the answer was reached.
Also known as: water calculator.
How to use the Water Intake Calculator
- Enter your weight.
- Select your activity level.
- See your daily water target.
Formula used
The water intake calculator is based on this formula:
Base = 35 ml x weight(kg) + activity adjustmentEach term in the formula corresponds to one of the inputs explained below. The calculator performs the arithmetic for you and shows every step so you can check the working by hand if you wish.
Worked example
Suppose you enter 70kg, moderate. The calculator works as follows:
| Inputs | 70kg, moderate |
|---|---|
| Working | 35x70 + 350 |
| Result | about 2.8 litres/day |
Step-by-step calculation
- Apply the formula:
Base = 35 ml x weight(kg) + activity adjustment - Substitute your values: 35x70 + 350
- Read the result: about 2.8 litres/day
Rough daily water guideline
| Body weight | Approx. water/day |
|---|---|
| 50 kg | ~1.75 litres |
| 60 kg | ~2.1 litres |
| 70 kg | ~2.45 litres |
| 80 kg | ~2.8 litres |
| 90 kg | ~3.15 litres |
Inputs explained
- Weight (kg) — the weight used in the calculation.
- Activity — the activity used in the calculation.
Understanding your result
- Recommended water — the calculated recommended water in litres/day.
- Glasses (250 ml) — the calculated glasses (250 ml).
Benefits and practical uses
The water intake calculator saves time and removes the risk of manual errors when you need to calculate water intake. It is useful for students, professionals and anyone who wants a fast, dependable answer. Results update the moment you press Calculate, work on any device, and can be copied or shared in a single click — and because the maths runs in your browser, your figures stay completely private.
Tips for an accurate result
- Keep all related inputs in the same units.
- Use the worked example above to confirm you are entering values in the right places.
- Review the assumptions below so the result fits your situation.
- Press Reset to clear everything and try a different scenario.
Common mistakes to avoid
- Entering values in the wrong unit (mismatched units give wrong answers).
- Leaving a required field empty — the calculator will ask you to fill it in.
- Treating the result as a diagnosis instead of a general guide.
Assumptions and limitations
- 35 ml/kg guideline.
- Adjust for climate, pregnancy and medical advice.
Frequently asked questions
Does this include water from food?
No. About 20% of fluid comes from food, so individual needs vary with climate and health.
How do I use the Water Intake Calculator?
Enter your values in the fields, then press the Calculate button to see the result. Use Reset to clear the form and start again. Nothing is calculated until you click Calculate.
What formula does the Water Intake Calculator use?
It uses the standard formula: Base = 35 ml x weight(kg) + activity adjustment. The full step-by-step working is shown with every result so you can verify it.
What information do I need to use the water intake calculator?
You need: weight, activity. Sensible example values are pre-filled so you can see how it works.
Is the Water Intake Calculator free to use?
Yes. Every DigiToolkit calculator is completely free, with no sign-up, no login and no usage limits.
Does the Water Intake Calculator work on mobile phones?
Yes. The calculator is mobile-first and works on phones, tablets and computers in any modern browser.
Do I need to install an app?
No. The water intake calculator runs directly in your web browser — there is nothing to download or install.
Is my data private when I use this calculator?
Yes. All calculations run inside your browser. The numbers you enter are never uploaded to a server or shared with anyone.
How accurate is the Water Intake Calculator?
It uses the generally accepted formula for water intake and computes to several decimal places. Results are accurate for the assumptions listed on this page.
Can I copy or share my result?
Yes. After calculating, use the Copy button to copy the result, or Share to copy the page link.
Why is nothing showing until I press Calculate?
By design, the calculator only computes when you press Calculate, so you can finish entering all your values first. Press Reset any time to clear everything.
What units does the Water Intake Calculator use?
It works with kg. Keep your inputs in consistent units for an accurate result.