How it works
U.S. Navy (men): %fat = 495 ÷ (1.0324 − 0.19077·log₁₀(waist − neck) + 0.15456·log₁₀(height)) − 450
This page keeps the calculation centered on one relationship: U.S. Navy (men): %fat = 495 ÷ (1.0324 − 0.19077·log₁₀(waist − neck) + 0.15456·log₁₀(height)) − 450. Inputs are normalized before the final display, which keeps mile, kilometer, pace, speed, or zone outputs from drifting because of rounding. Use the number as a consistent model output, then layer in terrain, weather, recovery, and race execution. Keep the fixed reference values in view: 495, 1.0324, 0.19077, 0.15456, 450, 34, 16, 68.
Sources
- U.S. Navy circumference method Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center, Report No. 84-11, 1984.
- ACE body-fat categories American Council on Exercise (ACE) body-fat norms — men: essential 2–5%, athletes 6–13%, fitness 14–17%, average 18–24%, above 25%+; women shifted ~8–10 points higher.
- Circumference vs. reference methods Tape-based estimates approximate hydrostatic weighing and DEXA but carry several points of error; they are best for tracking change over time, not single-reading precision.
FAQ
When should I use the body fat calculator?
Use it when you want a fast planning number before a run, race, workout, or gear decision. It gives you a consistent estimate without asking you to create an account.
What inputs matter most?
The best result comes from honest, current inputs. Recent race times, realistic body measurements, accurate workout data, and the correct unit setting matter more than perfect formatting.
How should I read the result?
Treat the output as a planning reference, not a promise. Use it to compare options, set a target range, or sanity-check your watch data before making the final call.
Does this work in miles and kilometers?
Yes. PacerRunning is written for US runners first, so miles are easy to use, but metric conversions are kept alongside them where the tool needs both views.
Why might my real-world result differ?
Terrain, wind, heat, sleep, fueling, training fatigue, and measurement error can all move the real outcome away from the estimate. This calculator cannot see those details.
Can beginners use it?
Yes. You do not need advanced training knowledge. Enter the numbers you know, read the result as a guide, and keep your effort comfortable when you are unsure.
Body Fat Calculator results are estimates from the entered data and the cited method. They are useful for planning and comparison, but they are not a diagnosis, prescription, guaranteed race result, or substitute for a coach or clinician.