Water Intake Calculator
Estimated daily water needs based on weight and exercise.
Your figures
Result
How to use this tool
- Enter your own figures over the defaults — Weight, Exercise per day.
- The answer updates as you type. There is no button, and nothing is sent anywhere.
- Change one input at a time to see how sensitive the answer is to it.
Roughly 20% of daily fluid comes from food. Needs rise substantially in heat, at altitude, during illness, and while pregnant or breastfeeding.
How it works
This takes 2 inputs — weight, exercise per day — and returns daily water, baseline, exercise allowance and note. The whole calculation happens in this page as you type: there is no submit button, no request, and nothing stored.
A worked example
Worked through with the figures the page already has in it: weight of 70 kg and exercise per day of 30 minutes, giving daily water of 2.66 litres. These numbers come from running the calculator’s own code, not from being typed in here, so they cannot drift away from what you see on screen.
Starting from:
- Weight: 70 kg
- Exercise per day: 30 minutes
| Result | Value |
|---|---|
| Daily water | 2.66 litres |
| Baseline | 2.31 L |
| Exercise allowance | 0.35 L |
| Note | A general guide. Needs vary with climate, health and diet. |
Water Intake Calculator — frequently asked questions
Is eight glasses a day right?
It is a rough rule with little evidence behind it. Needs scale with body size, activity, climate and diet.
Do tea and coffee count?
Yes. The mild diuretic effect of caffeine does not offset the fluid consumed. Food contributes around 20% as well.
Can I drink too much?
Rarely, but yes — hyponatraemia is dangerous and occurs mainly in endurance athletes drinking large volumes of plain water. Thirst is a reasonable guide for most people.
Is this calculator free?
Yes, with no account, no limits and no data collection. It runs entirely in your browser.
Should I rely on this for a financial or medical decision?
No. It is a planning estimate built on standard formulas and stated assumptions. For decisions that matter, speak to a qualified professional who can account for your full circumstances.
Is this calculator accurate?
The arithmetic is exact — it uses the standard formula. What limits accuracy is the assumptions: the figures you enter, and factors the formula does not model such as fees, taxes and rule changes.
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Nothing is sent anywhere. The figures you type stay in this page and are never transmitted or stored — how that works.
Disclaimer. The formula is exact; the answer is only as good as the figures and assumptions above. Not financial, tax, medical or legal advice. Full disclaimer.