Health calculators that show their working
Most calculators hand you one number. Ours name the formula behind it, put it next to every other published method so you can see how far they disagree for you, and say plainly who the result is wrong for. Every claim links to its source.
Try it: how much water do you need?
Enter your weight and see five common figures side by side, plus a schedule for your day.
Calculators that compare every method
Recently reviewed
Pages change when the evidence or our understanding of it does. The latest:
Each page shows the date it was last reviewed, and that date moves only when the page itself changes. Corrections are logged in our editorial policy.
Guides
Exercise how-tos
Reference charts
How we check a number
- Named formulas only. Every result names the equation and the people who published it. We do not invent our own.
- Coefficients from the source. Where we can read the original paper, we use its figures, not a copy of a copy. Where we cannot, the page says which secondary source we used.
- Links that still work. Every reference is checked automatically before each update; a dead link is treated as a defect.
- Limits stated up front. Each calculator says who its result does not apply to.
Frequently asked questions
Why do the methods give different answers?
Because they answer different questions. A survey-based figure describes what healthy people typically do; a dosing formula gives one reference number for a height; a rule of thumb is a rule of thumb. Seeing them together shows you how much certainty there really is behind any single number.
Who writes this, and are they a doctor?
Everything is written and edited by Waseem Sajad, who is not a doctor or licensed health professional. The site reports published guidance and links every source so you can check it yourself.
Is any of this medical advice?
No. Everything here is general educational information. If you have a medical condition, are pregnant, or take medication that affects fluids, weight or metabolism, follow your clinician rather than a calculator.
Does anything I type get stored?
No. The calculators run entirely in your browser and nothing you enter is sent anywhere.
Want to track it over time?
A free, ad-free habit tracker for water, sleep, mood, workouts and your cycle. It works without an account, and nothing leaves your device unless you sign in to sync.
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