How this works in your browser
This applies the US Navy circumference method, a formula derived by regression against more precise body composition measurements across a large population. It combines the logarithm of your circumference measurements with height, using different equations for men and women because fat distribution differs systematically. Being derived from population data is both its strength and its limit: it works well for typical body types and drifts for the very lean and the very muscular, whose proportions sit outside the range the formula was fitted to. Everything is computed in your browser, so measurements are never transmitted.
Body Fat Calculator vs. typical online calculators
| Feature | Body Fat Calculator (in-browser) | Typical online calculators |
|---|---|---|
| Where the maths runs | In your browser, on your device | Often posted to a server to compute |
| Your inputs are stored | Never - nothing is sent or saved | Frequently logged with your session |
| Works offline once loaded | Yes | No - needs a live connection |
| Ads inside the result area | None | Common on free calculators |
| Account required | No | Often, to save or export results |
| Usage limits | None - free, unlimited use | Sometimes capped per day |
Who uses Body Fat Calculator
Tracking body composition
Follow a trend over months using only a tape measure.
A better reading than BMI
Get an estimate that accounts for where mass is carried.
Fitness goal setting
Establish a baseline before starting a training or nutrition change.
Checking progress without a scale
See change when weight is stable but composition is shifting.
How to use Body Fat Calculator
- 1
Open the Body Fat Calculator
Go to tools.slaytic.com and open the Body Fat Calculator. No sign-up or account required.
- 2
Measure with a tape
Neck just below the larynx, waist at the navel, and for women the hips at their widest point.
- 3
Enter your measurements
Add height and gender alongside the circumference figures.
- 4
Track the trend
Measure the same way each time; the direction over months is more reliable than any single reading.
Frequently asked questions
How accurate is the US Navy method?
It is a reasonably accurate estimate for most body types using simple tape measurements, though it can be less precise for very lean or very muscular individuals compared to methods like DEXA scans.
Where exactly should I measure?
Neck: just below the larynx. Waist: at the navel. Hip (women only): at the widest point of the hips.
Is my measurement data stored?
No, the calculation happens entirely in your browser and nothing is saved or transmitted.
Why is this better than BMI?
Because it estimates composition rather than just mass. BMI cannot tell muscle from fat, so a lean athlete and a sedentary person of the same weight get the same score. Circumference measurements capture where mass is actually carried, which is the part that correlates with health risk.
How do I get consistent measurements?
Measure at the same time of day, ideally in the morning before eating, with the tape snug but not compressing the skin, and take each measurement twice. Inconsistent tape tension is the largest source of error, and a centimetre of difference at the waist shifts the estimate noticeably.
What are healthy body fat ranges?
Broadly, 8 to 19 percent for men and 21 to 32 percent for women is often cited as healthy, with athletes typically lower. These ranges vary by age and by source, so treat them as orientation rather than a target handed down.
How does this compare to a DEXA scan?
It is an estimate from a formula rather than a measurement of your body. DEXA and hydrostatic weighing are considerably more accurate but require equipment and cost money. The tape method's real strength is repeatability: measured consistently, the trend over months is informative even if the absolute number is off.