The scales cannot tell fat from muscle, which is why two people at the same weight can look and feel completely different. This calculator uses the US Navy method, which estimates body-fat percentage from height and circumference measurements, giving a far more useful picture of body composition than weight alone.
The Navy formula uses base-ten logarithms of the measurement differences and height, converted to a percentage with method-specific constants for men and women. Fitness trackers use it monthly to see whether training is actually changing composition, even when total weight barely moves. Everything runs in your browser: nothing you type is uploaded, stored or shared, and the tool is completely free with no sign-up required.
Quick Answer: Enter Gender, Height (cm), Neck (cm), Waist (cm), Hip (cm, women only) and get your estimated body-fat percentage instantly, with no sign-up and nothing uploaded.
Free Online Tool
Body Fat Calculator
Body-fat percentage from measurements, Navy method.
Results update when you click Calculate. Nothing you enter leaves your browser.
How to Use the Body Fat Calculator
- Enter the gender in the first field.
- Fill in the remaining fields: Height (cm), Neck (cm), Waist (cm), Hip (cm, women only).
- Check the values match what you intended, since a misplaced decimal or a wrong unit changes the answer.
- Click Calculate to see the result instantly in the result box.
- Read your estimated body-fat percentage and adjust any input to compare scenarios side by side.
Key Features
- Instant body fat calculator calculation with no waiting
- Private by design: everything runs in your browser
- Clear results showing the key figures together
- Works on desktop and mobile with the same layout
- Free to use, with no sign-up or account needed
Best Practices and Tips
- The Navy formula uses base-ten logarithms of the measurement differences and height, converted to a percentage with method-specific constants for men and women.
- Fitness trackers use it monthly to see whether training is actually changing composition, even when total weight barely moves.
- Round only the final answer, never the intermediate steps, so small rounding errors do not accumulate.
- Try a second scenario with slightly different inputs: comparing two results teaches more than any single number.
- If a result looks surprising, re-check the inputs first — a swapped value or a percentage entered as a whole number is the usual cause.
Common Mistakes to Avoid
- Mixing units, for example centimetres with metres or monthly with annual rates, which silently breaks the maths.
- Rounding intermediate values before the final step, which can shift the answer more than expected.
- Entering a percentage as a decimal, or a decimal as a percentage, and getting an answer out by a factor of one hundred.
- Trusting a single calculation for a big decision without testing a second, slightly different scenario.
Frequently Asked Questions
How does the Body Fat Calculator work?
It takes the values you enter and applies the standard calculation for this problem. The Navy formula uses base-ten logarithms of the measurement differences and height, converted to a percentage with method-specific constants for men and women. The result appears instantly, and changing any input recalculates everything, so you can explore different scenarios without starting over.
Is the Body Fat Calculator free?
Yes, completely free, with no sign-up, no account and no usage limit. You can run as many calculations as you like, on any device, and every feature of the tool is available from the first visit.
Do I need to sign up or install anything?
No. The tool runs entirely in your web browser, so there is nothing to install, no account to create and no software to update. Just open the page, enter your values and click Calculate.
Are my inputs private?
Yes. Every calculation happens locally in your browser, which means the numbers you enter are never sent to a server, stored in a database or shared with anyone. Closing the page removes them from view entirely.
How accurate is the Body Fat Calculator?
It is exact for the inputs and assumptions stated on the page, using the standard formula for this calculation. Results are estimates when the real world adds factors the tool cannot know, such as fees, taxes or individual variation, so treat them as a solid planning figure and check important decisions against official sources.