Body Fat Calculator
US Navy Method — just a tape measure, a bit of math, and a helpful estimate.
Measure at navel level
Yes, we need this. No, we won't ask why.
Estimated Body Fat
14.0%
Fitness
Reference Ranges (male)
The Navy method is a good estimate, but DEXA scans are the gold standard. This gets you in the ballpark.
About This Calculator
How It Works
The US Navy method estimates body fat by using circumference measurements as a proxy for fat tissue. Rather than measuring fat directly, it exploits the fact that leaner bodies tend to have proportionally smaller waist measurements relative to their neck and height. The formula feeds those values into a logarithmic equation developed from military data to produce a body fat percentage. It's widely used precisely because it requires only a tape measure — no gym equipment, no hydrostatic tank, no specialist.
The Formula
Men: 495 / (1.0324 - 0.19077×log10(waist-neck) + 0.15456×log10(height)) - 450. Women: similar with hip measurement added.
When to Use This
This is most useful for tracking body composition changes over time — watching your body fat percentage trend down over months is more meaningful than any single measurement. It's also a good complement to BMI: two people with identical BMIs can have very different body fat percentages depending on their muscle mass, and this calculator starts to reveal that distinction. Use it as a rough, repeatable benchmark rather than an absolute truth.
Limitations
The Navy method is sensitive to measurement technique — measuring your waist even 2-3cm off from the navel changes the result meaningfully. It also can't distinguish where fat is stored (visceral fat around organs carries more health risk than subcutaneous fat), and it becomes less accurate at body composition extremes (very lean athletes and people with very high body fat both see higher error rates). DEXA scans are the gold standard for precision; this gets you reliably in the ballpark.
Example
A man with 82cm waist, 38cm neck, and 178cm height: the formula gives approximately 14.1% body fat — solidly in the 'Athletic' category. The Navy method isn't lab-grade, but it's impressively accurate for just a tape measure.
Did You Know?
Essential body fat (the minimum needed for basic functioning) is about 2-5% for men and 10-13% for women. Athletes typically sit at 6-13% and 14-20% respectively. The rest of us are doing just fine.
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You Measured Today — Here's How to Automate It Going Forward
Calculating your body fat using the Navy method means you've already done the hard part: taking your measurements. But doing this manually every time — hunting for a tape measure, measuring at the right spots, doing the math — means most people only check once and forget about it.
A smart measuring tape changes that. It does the measuring, connects to an app, and logs your waist, hip, neck, and other measurements automatically every time you use it — so you can see your body composition trend over weeks and months without any manual tracking.
Our pick: the RENPHO Smart Body Measuring Tape
The RENPHO Smart Measuring Tape is the top-rated Bluetooth body tape measure on Amazon, and it's built for exactly this use case. It measures waist, hip, bust, arms, and more, syncs automatically to the RENPHO app (the same app used with RENPHO smart scales), and shows you a clear trend over time. Retractable, rechargeable, and accurate to 1mm. Under $25 — and it makes the difference between a one-off measurement and an actual body composition tracking habit.
If you've just calculated your body fat percentage and want to track it consistently going forward, this is the tool that makes it effortless.
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