What FitCalc is
FitCalc is a collection of nine single-purpose calculators covering body composition, energy and nutrition, hydration and training. Every tool runs entirely in your browser: you type your numbers, the math happens on your own device, and nothing is stored or sent anywhere. There is no account to create and nothing to install.
We built FitCalc because most fitness calculators are buried inside ad-heavy, slow, app-installing websites. Our goal is the opposite: a page that loads instantly, shows its formula, gives you a number you can trust, and lets you get on with your day.
The formulas we use
Every calculator publishes the exact equation it uses, so the math is fully checkable. Our formulas come from peer-reviewed and government sources:
- BMR and calorie needs — the Mifflin-St Jeor equation (1990), the formula most consistently validated against measured energy expenditure.
- Body fat — the U.S. Navy circumference method developed by Hodgdon and Beckett at the Naval Health Research Center (1984), with categories from the American Council on Exercise (ACE).
- BMI — the World Health Organization standard (weight in kg divided by height in meters squared) with WHO classification thresholds.
- Ideal weight — the four classic formulas: Devine (1974), Robinson (1983), Miller (1983) and Hamwi (1964), shown side by side because they were designed for different purposes and disagree by several kilograms.
- Water intake — 35 ml per kg of body weight from the U.S. National Academies' dietary reference intakes, plus exercise and climate adjustments.
- Heart rate zones — the standard 220−age maximum-heart-rate estimate, with the Karvonen (heart rate reserve) method when a resting heart rate is provided.
- Running pace and race predictions — the Riegel formula, the standard model for how pace changes with distance.
- One rep max — the Epley, Brzycki and Lombardi equations from submaximal lifting data.
Accuracy and limitations
These calculators are estimation tools, and we say so on every page. Formulas built on population averages cannot account for individual body composition, frame size, muscle mass, ethnicity or medical conditions. Our results have been cross-checked against the reference calculators used in research and clinical settings, and they agree to within rounding — but they are a starting point for a plan, not a prescription. For anything medical, speak to a clinician.
Privacy
FitCalc has no user accounts, no databases and no tracking scripts of its own. All calculations happen locally in your browser, so your inputs never leave your device. Third-party advertising (Google AdSense) may use cookies as described in our Privacy Policy.
Contact
Spotted a calculation error, have a formula question, or want to suggest a tool? Visit our contact page — we read everything.