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01Health & Fitness toolCalculated result
Water Intake Calculator
How much water to drink a day by weight, activity and climate.
100% FreeRuns instantlyNo watermark
- 1Enter detailsAdd the numbers for your scenario.
- 2CalculateVootkit updates the result instantly.
- 3ReviewCheck totals, notes and breakdowns.
Private by designProcessed on your device where possible.
Works on any deviceDesktop, tablet and mobile browsers.
No installationOpen the page and start working.
Always free coreUse the free plan for everyday tasks.
How to use Water Intake Calculator
Vootkit updates the result instantly.
02Check totals, notes and breakdowns.
03Copy the answer into your workflow.
04Your files stay private
Your work is processed locally in your browser where possible and is never added to a Vootkit upload library.
Learn more about privacyThe "eight glasses a day" rule is not from any study — it is a number that escaped into folklore. A slightly better estimate scales with body mass and adds for the two things that actually change requirement: sweating from exercise, and heat.
What Water Intake Calculator does
Starts from 35 ml per kilogram of body weight, adds 350 ml per 30 minutes of exercise, and adds a further 500 ml in a hot climate. Results are shown in litres, millilitres, and as 250 ml glasses.
Every one of those coefficients is a convention rather than a measured personal requirement — which is why the result is a starting estimate and not a prescription.
How the estimate is built
| Base | 35 ml per kg of body weight |
|---|---|
| Exercise | +350 ml per 30 minutes |
| Hot climate | +500 ml |
| Glass size used | 250 ml |
| Units | Metric (kg) or imperial (lb) |
| Exercise range | 0 to 600 minutes a day |
| Includes food? | No — food typically supplies 20–30% more |
| Includes tea/coffee? | They count toward total fluid |
Detailed steps
- Choose units and enter your weight.
- Add typical daily exercise minutes and pick your climate.
- Read the total, and treat it as a rough target rather than a quota.
Worth knowing
Thirst and urine colour are better guides than any formula — pale straw is about right. The calculation ignores water in food, which typically supplies another 20–30%, so someone eating a lot of fruit and vegetables genuinely needs less from the glass than this suggests.
Frequently Asked Questions
Where does 35 ml per kg come from?
It is a widely used clinical rule of thumb for adult maintenance fluid, not a finding from a specific trial. Individual requirement varies with kidney function, medication, diet and activity, none of which this can see.
Do tea and coffee count?
Yes. The idea that caffeine dehydrates you at normal intakes has not held up — the fluid in a cup of coffee counts toward your total. Alcohol is genuinely different and increases fluid loss.
Can I drink too much water?
Yes, and it is dangerous. Drinking far beyond thirst over a short period can dilute blood sodium, a condition called hyponatremia, which is a medical emergency. This tool estimates a daily total to spread across the day, not a volume to consume quickly.
Should I follow this if I have a health condition?
No. Kidney disease, heart failure and several medications come with specific fluid instructions that override any general formula. Follow your clinician’s advice, not this.
Is Water Intake Calculator free?
Yes. The Vootkit free plan includes 5 tool runs a day. Upgrade to Vootkit Pro for unlimited daily use, an ad-free workspace and saved workflows.
Are my files uploaded?
No. Water Intake Calculator runs entirely in your browser — your file is processed on your own device and never sent to a server. There is nothing for us to store or delete.
Do I need to install anything?
No. Water Intake Calculator works in any modern browser on desktop, tablet or phone. Open the page and start.
How often can I use it? Is there a daily limit?
On the free plan you get 5 tool runs a day. When you reach the limit you'll see a prompt to upgrade, and it resets the next day. Vootkit Pro removes the cap entirely for unlimited daily use.
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