Body Fat Calculator
All you need is a tape measure. Pick the US Navy method or the Army tape test — both run in your browser, and both are usually within 3–4 percentage points of a DEXA scan.
Last updated October 25, 2026
How to use this calculator
- Pick a method: US Navy (waist-based, the classic) or the US Army tape test (AR 600-9, men use neck and height only).
- Measure in the morning, before eating, with relaxed muscles — the tape snug but not digging in.
- Take each measurement 2–3 times and average them, then enter the averages with your height and weight.
How the Navy method works
The US Navy circumference method (Hodgdon & Beckett, 1984) estimates body fat from the relationship between your height and key circumferences. In inches:
Men: %BF = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76Women: %BF = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387Validation studies against hydrostatic weighing show standard errors around 3–4% body fat — not perfect, but excellent for tracking change over time when you measure the same spots the same way.
The Army tape test (AR 600-9)
The US Army's circumference method from Regulation AR 600-9 trades a little accuracy for speed: men are measured at the neck and height only — no waist tape — while women use the same waist, hip and neck measurements as the Navy method:
Army men: %BF = 86.010 × log₁₀(neck) − 70.041 × log₁₀(height) + 36.76Because it drops the waist measurement, the male Army formula is known to run generous (typically a few points lower than Navy or DEXA) — it is a screening pass/fail tool, not a precision instrument. Pick it if you want the number the Army would record for you; pick Navy if you want the tighter estimate.
Army height-weight (HT/WT) screening: the allowable body-fat table
The Army's “htwt” check is a two-step process under AR 600-9: first your weight-for-height is screened against an entry table; if you exceed it, you move to the tape test — where the allowable body-fat ceiling depends on age and sex:
| Age group | Male max %BF | Female max %BF |
|---|---|---|
| 17–20 | 20% | 30% |
| 21–27 | 22% | 32% |
| 28–39 | 24% | 34% |
| 40 and over | 26% | 36% |
Exceeding the screening weight does not mean failing — it only triggers the tape test, and a muscular soldier with a low tape measurement passes. That is exactly why the circumference method exists: it separates mass from fat. Run your numbers above and compare against your age band.
What the numbers mean
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletic | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
Ranges per the American Council on Exercise; “essential fat” is the floor needed for basic physiology — it is not a target.
Frequently asked questions
How do I calculate body fat percentage?
The practical at-home options are circumference formulas like the ones on this page (a tape measure and two minutes), skinfold calipers, or a scale with bioelectric impedance. For a reference-grade number you need a DEXA scan. For tracking change over time, the tape methods are the best effort-to-accuracy trade-off.
How accurate is the tape method compared to DEXA?
Expect results within about 3–4 percentage points of a DEXA scan. The number itself may be slightly off, but if you measure the same spots each time, the trend is reliable.
What is the difference between the Navy and Army body fat formulas?
For women they are identical. For men, the Navy formula uses waist and neck circumference; the Army tape test (AR 600-9) uses neck and height only, which makes it faster but several points more generous. Use Army if you want the military's screening number, Navy for a tighter estimate.
Tips for consistent measurements?
Same time of day, same spots, tape level and snug without compressing skin, and average two or three readings. Consistency matters more than perfection.
How often should I remeasure?
Every 2–4 weeks. Body fat changes slower than scale weight, and measurement noise means daily readings would only confuse you.