The Body Fat Calculator is a free tool that helps you calculate body fat using the formula US Navy method using log10 of body circumferences and height. Enter your values above and press Calculate to get body fat instantly, with a full step-by-step breakdown.
What is the Body Fat Calculator?
The body fat calculator is a free online tool that helps you calculate body fat quickly and accurately. It applies the standard formula US Navy method using log10 of body circumferences and height to the values you enter and, when you press Calculate, displays the result together with a clear, step-by-step explanation of how the answer was reached.
Also known as: body fat percentage calculator, fat percentage calculator, fat calculator.
How to use the Body Fat Calculator
- Choose gender.
- Measure height, neck and waist (and hip for women).
- See your estimated body-fat percentage.
Formula used
The body fat calculator is based on this formula:
US Navy method using log10 of body circumferences and heightEach term in the formula corresponds to one of the inputs explained below. The calculator performs the arithmetic for you and shows every step so you can check the working by hand if you wish.
Worked example
Suppose you enter Male, 170cm, neck 38, waist 85. The calculator works as follows:
| Inputs | Male, 170cm, neck 38, waist 85 |
|---|---|
| Working | Navy formula |
| Result | Body fat about 18% |
Step-by-step calculation
- Apply the formula:
US Navy method using log10 of body circumferences and height - Substitute your values: Navy formula
- Read the result: Body fat about 18%
Inputs explained
- Gender — the gender used in the calculation.
- Height (cm) — the height used in the calculation.
- Neck (cm) — the neck used in the calculation.
- Waist (cm) — the waist used in the calculation.
- Hip (female) (cm) — the hip (female) used in the calculation.
Understanding your result
- Body fat — the calculated body fat in %.
Benefits and practical uses
The body fat calculator saves time and removes the risk of manual errors when you need to calculate body fat. It is useful for students, professionals and anyone who wants a fast, dependable answer. Results update the moment you press Calculate, work on any device, and can be copied or shared in a single click — and because the maths runs in your browser, your figures stay completely private.
Tips for an accurate result
- Keep all related inputs in the same units.
- Use the worked example above to confirm you are entering values in the right places.
- Review the assumptions below so the result fits your situation.
- Press Reset to clear everything and try a different scenario.
Common mistakes to avoid
- Entering values in the wrong unit (mismatched units give wrong answers).
- Leaving a required field empty — the calculator will ask you to fill it in.
- Treating the result as a diagnosis instead of a general guide.
Assumptions and limitations
- US Navy circumference method.
- Accurate tape measurements required.
Frequently asked questions
How accurate is the Navy method?
It is a reasonable estimate (+/- 3-4%) but less precise than DEXA scans.
How do I use the Body Fat Calculator?
Enter your values in the fields, then press the Calculate button to see the result. Use Reset to clear the form and start again. Nothing is calculated until you click Calculate.
What formula does the Body Fat Calculator use?
It uses the standard formula: US Navy method using log10 of body circumferences and height. The full step-by-step working is shown with every result so you can verify it.
What information do I need to use the body fat calculator?
You need: gender, height, neck, waist, hip (female). Sensible example values are pre-filled so you can see how it works.
Is the Body Fat Calculator free to use?
Yes. Every DigiToolkit calculator is completely free, with no sign-up, no login and no usage limits.
Does the Body Fat Calculator work on mobile phones?
Yes. The calculator is mobile-first and works on phones, tablets and computers in any modern browser.
Do I need to install an app?
No. The body fat calculator runs directly in your web browser — there is nothing to download or install.
Is my data private when I use this calculator?
Yes. All calculations run inside your browser. The numbers you enter are never uploaded to a server or shared with anyone.
How accurate is the Body Fat Calculator?
It uses the generally accepted formula for body fat and computes to several decimal places. Results are accurate for the assumptions listed on this page.
Can I copy or share my result?
Yes. After calculating, use the Copy button to copy the result, or Share to copy the page link.
Why is nothing showing until I press Calculate?
By design, the calculator only computes when you press Calculate, so you can finish entering all your values first. Press Reset any time to clear everything.
What units does the Body Fat Calculator use?
It works with cm. Keep your inputs in consistent units for an accurate result.