Body Fat Calculator
Your details
Result
Body fat
- Category
- Fitness
- Fat mass
- 29.7 lb
- Lean body mass
- 150.3 lb
- BMI for comparison
- 25.8 (overweight range)
- Working
- 86.010 × log₁₀(34 − 15.5) − 70.041 × log₁₀(70) + 36.76 = 16.52%
- The Navy method is an estimate from tape measurements, and its accuracy is typically within 3 to 4 percentage points of a DEXA scan — sometimes worse at the extremes. Treat 16.5% as a range of roughly 13% to 20%, not a precise figure. It is most useful for tracking change over time with consistent technique, where the error largely cancels.
- Lean body mass of 150.3 lb is the figure worth tracking alongside the percentage. During weight loss the goal is for fat mass to fall while lean mass holds — a percentage alone cannot tell you which is changing.
- BMI for these figures is 25.8, which would be read as overweight. BMI uses only height and weight, so it cannot distinguish muscle from fat — which is why a muscular athlete can be classed overweight by BMI while measuring a low body fat percentage.
Reference ranges — men
Categories from the American Council on Exercise. They are population reference ranges, not individual targets, and essential fat differs between the sexes.
| Category | Body fat |
|---|---|
| Below essential fat | under 5% |
| Athletic | 5–13% |
| Fitness (yours) | 13–17% |
| Average | 17–24% |
| Above average | over 24% |
What the percentage means in pounds
The same body fat percentage at different weights, for context.
| Weight | Fat mass | Lean mass |
|---|---|---|
| 160 lb | 26.4 lb | 133.6 lb |
| 170 lb | 28.1 lb | 141.9 lb |
| 180 lb (yours) | 29.7 lb | 150.3 lb |
| 190 lb | 31.4 lb | 158.6 lb |
| 200 lb | 33 lb | 167 lb |
How do you calculate body fat percentage?
The US Navy method estimates body fat from tape measurements. For men it is 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76. A man of 70 inches with a 34 inch waist and 15.5 inch neck measures about 16.5%.
men: %BF = 86.010 · log₁₀(waist − neck) − 70.041 · log₁₀(height) + 36.76 women: %BF = 163.205 · log₁₀(waist + hip − neck) − 97.684 · log₁₀(height) − 78.387- waist
- At the navel for men, the narrowest point for women
- neck
- Just below the larynx
- hip
- At the widest point; female formula only
- log₁₀
- Base-10 logarithm — the relationship is not linear
The Navy formula is a regression fitted to circumference measurements against hydrostatic weighing, which is why the coefficients look arbitrary — they are empirical, not derived. The logic is that the waist-to-neck difference captures central fat deposition while height normalises for frame size, and the female version adds the hip because fat distribution differs. Two consequences follow from it being a regression. First, accuracy is limited: it typically lands within 3 to 4 percentage points of a DEXA scan, and it degrades at the extremes of body composition, so a single reading is a range rather than a number. Second, measurement technique dominates the error. A half-inch difference in where the tape sits on the waist moves the result by around a full percentage point, which means consistency matters more than precision — the method is far more reliable for tracking change over months than for establishing a true value today. What it does offer over BMI is the ability to distinguish fat from muscle at all. BMI uses only height and weight, so a muscular athlete reads as overweight; a circumference method does not make that mistake.
- Measure your height in inches without shoes.
- Measure the waist at the navel, or narrowest point for women.
- Measure the neck just below the larynx.
- Women also measure the hip at its widest point.
- Apply the formula for your sex using base-10 logarithms.
- Multiply by your weight for fat mass in pounds.
Worked example: A man 70 inches tall with a 34 inch waist, 15.5 inch neck, weighing 180 lb
A man 70 inches tall with a 34 inch waist, 15.5 inch neck, weighing 180 lb
The waist-to-neck difference is 34 − 15.5 = 18.5 inches, whose base-10 logarithm is 1.2672. The logarithm of the 70 inch height is 1.8451. Substituting: 86.010 × 1.2672 = 108.99, and 70.041 × 1.8451 = 129.22, so the result is 108.99 − 129.22 + 36.76 = 16.52%. That falls in the fitness band for men, between the 13% athletic threshold and the 17% upper fitness limit. At 180 lb it works out as 29.7 lb of fat mass and 150.3 lb of lean mass, and the lean figure is the one worth tracking — during weight loss you want fat mass to fall while lean mass holds. For contrast, BMI on the same height and weight is 25.8, which reads as overweight. Both describe the same body, and the disagreement is the point: BMI cannot distinguish muscle from fat, while a tape measure at least attempts to.
What each body fat input means
- Sex
- The Navy formula uses different coefficients and different measurement sites by sex — the female version includes the hip measurement.
- Height
- Standing height in inches, without shoes.
- Waist circumference
- For men, measured at the navel. For women, at the narrowest point. Measure after a normal exhale with the tape snug but not compressing.
- Neck circumference
- Just below the larynx, with the tape sloping slightly downward at the front.
- Hip circumference
- At the widest point. Used in the female formula only.
- Weight
- Used to convert the percentage into fat mass and lean mass in pounds, which is the more useful figure to track over time.
What this body fat does not account for
- This is an estimate, typically within 3 to 4 percentage points of a DEXA scan, and less reliable at the extremes of body composition. A single reading is a range, not a figure.
- Measurement technique dominates the error. A half-inch difference in waist placement moves the result by about a percentage point, so consistent technique matters more than precision.
- The method is far better for tracking change over months with the same technique than for establishing a true value on one day, because consistent error largely cancels.
- The waist must measure larger than the neck, since the formula takes a logarithm of the difference. Measurements that violate this produce no valid result.
- Essential body fat differs by sex — roughly 2 to 5% for men and 10 to 13% for women — and dropping below it carries real health consequences.
- Reference categories are population ranges, not individual targets. Athletic performance, health and appearance do not all optimise at the same percentage.
- The formula was fitted on adult military populations and is less applicable to children, pregnant women, bodybuilders and the very elderly.
- BMI and body fat percentage frequently disagree, and that is expected. BMI uses only height and weight, so it reads muscle as excess weight.
Frequently asked questions
What is a healthy body fat percentage?
Reference ranges put men's fitness band at 14 to 17% and average at 18 to 24%; for women, fitness is 21 to 24% and average 25 to 31%. These are population ranges rather than individual targets.
How accurate is the Navy body fat method?
Typically within 3 to 4 percentage points of a DEXA scan, with more error at the extremes. It is most useful for tracking change with consistent technique rather than establishing an exact value.
Why is my body fat percentage different from my BMI category?
Because BMI uses only height and weight and cannot distinguish muscle from fat. A muscular person often reads as overweight by BMI while measuring a low body fat percentage.
Where exactly do I measure my waist?
At the navel for men, and at the narrowest point for women. Measure after a normal exhale with the tape snug but not compressing the skin, and use the same spot every time.
What is lean body mass?
Everything that is not fat — muscle, bone, organs and water. It is worth tracking alongside the percentage, because during weight loss the goal is losing fat while preserving lean mass.
What is the most accurate way to measure body fat?
DEXA scanning and hydrostatic weighing are the practical reference standards, and both require a facility visit. Calipers, bioimpedance scales and circumference formulas are all estimates with meaningfully wider error bands, though they track change adequately.
Sources and review
- Percent body fat norms for men and women — American Council on Exercise
Last reviewed .