The short answer
How the tape method works
Instead of measuring fat directly, the tape method plugs a few body measurements into an equation built from people who were also measured in a lab. The traditional Navy method uses your neck, waist and height, plus hips for women. The Army has since moved to a one-site method that uses only your waist at the navel and your body weight 2. You can try both with our free body fat calculator.
The appeal is obvious: a tape measure costs a few dollars and a DEXA scan, the X-ray based body composition scan used as the reference in most of this research, means booking an appointment. The question is how much accuracy you give up.
How close is it to a DEXA scan?
When 1,407 Army recruits were measured both ways at the start of basic training, the traditional circumference equation underestimated body fat by about 6 percentage points on average, in both women and men 1. So someone whose DEXA scan reads 26% might see about 20% from the tape.
A larger study of 1,904 soldiers compared the old equation with the new one-site equation against DEXA. Both tape methods underestimated body fat. The average gap from DEXA was 2:
| Equation | Men | Women |
|---|---|---|
| Traditional Navy tape | 5.88 points | 4.39 points |
| Army one-site | 4.38 points | 4.59 points |
So the newer equation was clearly better for men and about the same for women. Its other advantage is consistency: its underestimate was similar across sex, age and race 2. The study that built the one-site equation found the same pattern, with larger accuracy gains for men than for women 3.
The bigger problem: tracking change
For most people the real question is not "what is my exact number" but "is it going down". That is where the traditional tape method did worst. Over 8 weeks of basic training, the same recruits were measured again1:
| Change over 8 weeks | DEXA | Tape method |
|---|---|---|
| Women | Down 4.0 points | No change (0.0) |
| Men | Down 3.3 points | Down 2.2 points |
In women, the tape method missed the fat loss entirely; in men it caught about two thirds of it. The researchers concluded that circumference-based body fat may not be an appropriate tool for tracking body composition changes over a short period 1.
What about one individual reading?
Averages hide a lot. In a study of 96 adults, the Army one-site equation matched DEXA almost exactly on average, but the limits of agreement, the range most individual differences fall within, were about 10 percentage points4. Compared with a four-compartment model, the most rigorous lab method, it overestimated body fat by 1.3 points on average and showed a bias that changed with body fat level 4. The authors described group-level performance as acceptable but raised concerns about using it for individuals.
How to get the most out of it
The method is still useful if you use it for what it is good at: a cheap, repeatable check that you do the same way each time. Three habits help:
Measure the same way every time. The Navy's own procedure measures on bare skin with a non-stretch tape, snug without compressing, at the end of a normal breath out, and takes each measurement twice 5.
Watch the waist, not just the percentage. Given how poorly the percentage tracked change in the recruit study 1, the raw waist measurement and your weight trend are often the more honest signals. Our calculator saves both alongside the estimate.
Do not mix methods. The two equations give different numbers for the same body, so compare Army with Army and Navy with Navy. If you ever get a DEXA scan, treat it as its own line rather than a correction to your tape readings.
Try this workout
Measure the same way every time
Who it is for: Anyone using the tape method to track their body over weeks and months.
- 1Same conditions. Morning, before eating, after using the bathroom. Same day of the week each time.
- 2Tape on bare skin. A non-stretch tape, level and snug without pressing in, read at the end of a relaxed breath out 5.
- 3Twice per site. Go round the sites in turn, then round again, so each is measured twice. If the two readings differ by more than an inch, take a third and average the two closest 5.
- 4Every 2 to 4 weeks. Save your result, and judge the trend over several readings, not one.
Put it into practice
Sources
All research- 1Body composition changes during 8 weeks of military training are not accurately captured by circumference-based assessmentsFoulis et al., 2023. Frontiers in Physiology 14:1183836.
- 2Science behind policy: implementing a modern circumference-based body fat equation with a physical fitness threshold is associated with lower musculoskeletal injury riskMcClung et al., 2025. International Journal of Obesity 49(4):723-730.
- 3Development and cross-validation of a circumference-based predictive equation to estimate body fat in an active populationTaylor et al., 2024. Obesity Science & Practice 10(2):e747.
- 4Body composition estimation from mobile phone three-dimensional imaging: evaluation of the USA army one-site methodFlorez et al., 2024. British Journal of Nutrition 132(9):1143-1151.
- 5Guide 4: The Body Composition Assessment (BCA)U.S. Navy, 2016. Navy Physical Readiness Program (OPNAVINST 6110.1 series), January 2016.
General fitness information, not medical advice. If you have an injury or a health condition, check with a professional before starting a new kind of training.