Body Fat Percentage Calculator
Estimate your body fat percentage using the US Navy method — a tape-measure technique that's surprisingly accurate for most people. Enter a few measurements to see your estimated body fat percent, fitness category, and breakdown of lean mass versus fat mass in pounds.
Your Body Fat Percentage
Body fat categories (American Council on Exercise)
| Category | Men | Women |
|---|---|---|
| Essential fat | 2-5% | 10-13% |
| Athletes | 6-13% | 14-20% |
| Fitness | 14-17% | 21-24% |
| Acceptable | 18-24% | 25-31% |
| Obese | 25%+ | 32%+ |
How to measure correctly
Neck: Just below the larynx (Adam's apple), keeping the tape level. Waist: Men — at the navel; Women — at the narrowest point. Hips (women only): Around the widest part of your buttocks. Use a non-stretching tape, breathe normally, and don't pull tight enough to compress skin.
How This Calculator Works
This calculator uses the US Navy circumference method, which estimates body fat from a few tape measurements and your height using logarithmic equations. For men the formula is %BF = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76, with all measurements in inches. For women it adds the hip measurement: %BF = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387. Once it has your body fat percentage, the tool multiplies it by your bodyweight to split your total into fat mass and lean mass.
A Worked Example
Take a man who is 5′10″ (70 inches) with a 34-inch waist and a 15-inch neck. The waist-minus-neck difference is 19 inches. Plugging in: 86.010 × log₁₀(19) − 70.041 × log₁₀(70) + 36.76 = (86.010 × 1.279) − (70.041 × 1.845) + 36.76 = 110.0 − 129.2 + 36.76 = 17.5% body fat, which lands in the fitness category. If he weighs 170 pounds, that is about 29.8 lb of fat mass and 140.2 lb of lean mass. Shaving an inch off the waist would drop the estimate to roughly 15.5 percent.
What Affects Your Result
- Measurement technique: A tape pulled tight or held at the wrong spot is the biggest source of error; a half-inch on the waist visibly moves the result.
- Time of day and hydration: Bloating, a full stomach and water retention all change waist circumference, so measure consistently.
- Fat distribution: The formula assumes average storage patterns; if you carry fat unusually high, low or in the limbs, the estimate drifts.
- Sex: Men and women use different equations because of where they store fat — using the wrong one gives a nonsense answer.
- Muscularity: A very thick neck from heavy training can shrink the waist-neck gap and slightly underestimate fat in lean athletes.
- Posture and breathing: Sucking in or standing tall changes circumference; stay relaxed and breathe normally.
Frequently Asked Questions
How accurate is the US Navy body fat method?
For most people the tape-measure method lands within about 3 to 4 percent of a DEXA scan, which is good for a free, equipment-free estimate. Accuracy drops for very lean or very obese individuals and for those with unusual fat distribution, because the formula assumes an average relationship between circumference and total fat.
Why does the calculator ask women for a hip measurement but not men?
The US Navy developed two separate equations because men and women store fat differently. The male formula relies on the gap between waist and neck, while the female formula adds hip circumference because women carry proportionally more fat around the hips and thighs. Including the hip measurement makes the female estimate considerably more accurate.
What body fat percentage should I aim for?
It depends on your goals and sex. Using American Council on Exercise ranges, men in the fitness category sit around 14 to 17 percent and women around 21 to 24 percent. Athletes go lower, but chasing very low body fat is hard to sustain and is not automatically healthier. Pick a range you can maintain comfortably.
How do I measure myself for the most accurate result?
Use a flexible, non-stretching tape and measure on bare skin first thing in the morning before eating. Keep the tape level and snug without compressing the skin, take each measurement two or three times and average them. Measure the neck just below the larynx, the waist at the navel for men or the narrowest point for women, and the hips at the widest point of the buttocks.
Tape-measure body fat is an estimate, not a clinical measurement — DEXA, hydrostatic weighing and air-displacement methods are more precise. Use this for tracking trends over time, and treat it as educational information rather than medical advice.