How this started
I wanted to check my BMI. Simple enough request. Every site I found either made me create an account, showed five popups before I could see the result, ran slow, or paywalled the more detailed tools. I got annoyed. I built a clean BMI calculator for myself instead — one page, no friction, instant result.
Then I needed my TDEE. Same problem, same solution. Then macros. Then someone I knew asked if I could add a body fat calculator. Then a water intake one. At some point I had 10 calculators and decided I might as well put them somewhere people could use them. I bought the domain quickbmi.in in a hurry — because it was available and I was impatient — and launched with whatever I had.
The site is now called FitMetrics and has 36 calculators. The domain name still says quickbmi. I've made peace with this.
What I actually built here
Every calculator uses a real, named formula — not something I invented. BMR and TDEE use the Mifflin-St Jeor equation. Body fat uses the US Navy circumference method. Ideal weight uses the Devine formula. One rep max uses Brzycki and Epley averaged together. Heart rate zones use the Karvonen formula. I list the formula name on each calculator page so you can look it up yourself if you want to verify it.
Results are estimates. I say this clearly because it's true, and I'd rather be honest about it than pretend a circumference measurement is as accurate as a DEXA scan. Use the numbers as starting points, check them against reality over a few weeks, and adjust.
No data is stored. Everything runs in your browser. When you close the tab, your numbers are gone. I have no server collecting your weight and height — I genuinely don't want that responsibility.
What this isn't
This is not a medical service. The calculators are not a substitute for talking to a doctor. I'm a developer, not a clinician. If something in your results worries you, or you have a condition that affects your nutrition or fitness, please talk to someone qualified. I've tried to be accurate and honest in everything here, but these are general tools for generally healthy adults, and individual circumstances vary enormously.
This is also not a content farm trying to rank for every health keyword. The blog posts exist because people asked questions that were worth answering properly. I'd rather write one genuinely useful guide than ten thin ones.
What's next
I keep adding calculators when I find a gap that isn't being filled well elsewhere. If there's a tool you need that isn't here, use the contact form — I read every message and have added several calculators based on requests. If something is broken or giving wrong results, I want to know that too.
The site will stay free. No subscription tier is coming. No premium features. That's the whole point.
Questions, bugs, or suggestions?
Use the contact form. I reply personally, usually within a day or two.
The formulas used across the site
For anyone who wants to verify the maths:
- BMR / TDEE — Mifflin-St Jeor equation (1990), validated as most accurate for general population
- Body fat % — US Navy circumference method (Hodgdon & Beckett, 1984)
- Ideal weight — Devine formula (1974), originally developed for drug dosing
- Lean body mass — Boer formula (1984)
- One rep max — Average of Epley (1985) and Brzycki (1993) formulas
- Heart rate zones — Karvonen formula using heart rate reserve
- Body surface area — Mosteller formula (1987)
- BMI — Standard WHO formula: weight (kg) ÷ height² (m)
- Due date — Naegele's rule adjusted for cycle length
- Pregnancy weight gain — Institute of Medicine (IOM) guidelines
The calculators and articles here are for educational purposes only — not medical advice. Always consult a qualified healthcare professional before making decisions about your health. Full details in the disclaimer.