Body Fat Percentage Calculator
A real estimate using just a tape measure -- the U.S. Navy circumference method.
Estimated body fat percentage
18.0%
Category: Fitness
Essential fat
2-5%
Athletes
6-13%
Fitness
14-17%
Average
18-24%
Obese
25%+
Worked example
Male: 5'9", neck 15 in, waist 34 in
86.010 × log₁₀(34 − 15) − 70.041 × log₁₀(69) + 36.76 = 18.0%, which the ACE chart calls fitness. At 170 lb that is about 31 lb of fat and 139 lb of lean mass.
Female: 5'5", neck 13 in, waist 30 in, hips 38 in
163.205 × log₁₀(30 + 38 − 13) − 97.684 × log₁₀(65) − 78.387 = 28.6%, which the ACE chart calls average.
Waist is the number that moves the result. For the male example, one extra inch at the waist adds about 1.9 percentage points; one inch on the neck removes about 2.0. Measure both the same way every time and the trend is trustworthy even if the absolute number is a couple of points off.
What the categories mean
The bands are the American Council on Exercise (ACE) ranges the calculator reports. "Essential" is the minimum for normal physiological function, not a target; "athletes" is where visible abdominal definition usually starts; "average" is where most healthy adults sit.
| Men | Body fat |
|---|---|
| Essential fat | 2-5% |
| Athletes | 6-13% |
| Fitness | 14-17% |
| Average | 18-24% |
| Obese | 25%+ |
| Women | Body fat |
|---|---|
| Essential fat | 10-13% |
| Athletes | 14-20% |
| Fitness | 21-24% |
| Average | 25-31% |
| Obese | 32%+ |
Measuring so the number means something
- Morning, before eating, after the bathroom. A meal or a bloated day adds an inch at the waist and two points to the result.
- Tape level and snug, not pulled tight. It should sit flat against skin all the way round without denting it. Pulling tight is the most common way to get a flattering, wrong number.
- Same landmarks every time. Waist at the narrowest point (or the navel if there is none), neck just under the larynx, hips at the widest point. Mark them mentally and do not shop around for the best-looking line.
- Track every two to four weeks, not daily. Real fat loss shows up in the waist measurement at roughly a quarter to half an inch a month; daily readings are noise.
- Pair it with the scale. Weight down and waist down is fat loss. Weight flat and waist down is recomposition. Weight down and waist flat is worth a look at protein and training.
Keep going
- A higher body fat reading usually means a deficit makes sense first; the macros-for-cutting page sets that deficit and protein floor. Macros for Cutting
- On the leaner end of the reading, the macros-for-bulking page sizes a surplus built to favor muscle over fat. Macros for Bulking
Frequently Asked Questions
How accurate is a tape-measure body fat estimate?
The U.S. Navy circumference method used here is generally accurate within a few percentage points for most people -- close enough to track real trends over time, though a DEXA scan or hydrostatic weighing will be more precise for an exact number.
Why does the formula need different measurements for men and women?
Men and women tend to carry fat differently (more around the waist for men, more around the hip for women), so the published Navy formula uses a different measurement set and set of constants for each to stay accurate.
Where should I measure my waist and neck?
Waist: at the narrowest point, or at the navel if there's no clear narrowing. Neck: just below the larynx (Adam's apple), tape sloped slightly downward at the front. Measure snug but not compressed.
Why does my smart scale give a different number?
Bioimpedance scales estimate body fat from how a tiny current travels through you, which shifts with hydration, a recent meal, a workout, even foot calluses. Day-to-day swings of 3-5 points are normal on a scale. The tape method has its own error but is not affected by hydration in the same way, so its trend is steadier.
How fast can body fat percentage realistically drop?
Around 0.5-1 percentage point a month for most people in a sensible deficit: a 170 lb person at 20% has 34 lb of fat, and losing 1 lb of fat a week moves the percentage about half a point. Faster drops on a scale are usually water. Re-measure every 2-4 weeks and expect the waist tape to move about a quarter to half an inch a month.