About Us

Fat-Calculator.com is an informational fitness website built by a small team of developer-enthusiasts. We make free, easy-to-use online calculators that give approximate fitness-related estimates — such as BMI, body fat percentage, and energy needs — based on well-known formulas published in openly available sources. The tools are free, work in your browser, and require no sign-up.

What This Site Is

We are an information and reference resource, not a health or medical service. Our calculators are educational tools for general interest: they let you quickly run rough, illustrative numbers from publicly available fitness formulas. They are not measurements, not assessments, and they are not intended to tell you anything about your individual health. Any interpretation, diagnosis, or decision in the area of health belongs with qualified doctors and healthcare professionals — not with this website.

Where Our Formulas Come From

We are developers, so we don't create formulas ourselves. Each calculator simply implements a publicly available equation, and we link the open sources it is based on directly on that calculator's page so you can read the originals yourself. When we build a tool, we re-check the math and test it across a range of inputs so the calculator behaves consistently with the published formula. The open references used by each tool include:

Body Fat Calculator — based on the publicly available Deurenberg BMI formula, with category ranges referencing openly published World Health Organization (WHO) and American Council on Exercise (ACE) materials.
U.S. Navy Body Fat Calculator — based on the publicly documented U.S. Navy circumference (tape-measure) method (Hodgdon & Beckett), with reference ranges from openly published ACE materials.
Muscle Mass Calculator — based on publicly available work by Janssen et al. and Lee et al., the Boer lean-body-mass formula, and the Mifflin–St Jeor equation.
Calorie Deficit Calculator — based on the publicly available Mifflin–St Jeor equation and the commonly cited ~7,700 kcal/kg rule of thumb.

Each calculator page lists the open sources for the formula it uses. Where a formula is known to be only a rough approximation — for example, BMI-based estimates for very muscular people — we note that openly on the page so the limits are clear.

Why We Build These Tools

Our aim is simple: offer handy, free fitness calculators that anyone can use for general interest, with the underlying formulas and their open sources shown plainly. We'd rather be transparent about what an estimate can and can't tell you than overstate it.

Please Note

All calculators and content on Fat-Calculator.com are provided for general informational purposes only. They produce approximate estimates from publicly available formulas, they are not medical advice, and they are not a substitute for professional diagnosis, treatment, or consultation. Always consult a qualified physician or healthcare provider before making any decisions related to diet, exercise, or weight.

Feedback

We keep improving existing tools and adding new ones. If you spot something that looks off or have a suggestion, please reach out through our contact page.