17 Fit Calculators Body fat calculator
Body fat calculator your body fat percentage from a tape measure
Measure your neck and waist (and hips, for women) and enter your height. You’ll see your body fat percentage by the US Navy method, the same formula as in 17 Fit, and your waist‑to‑height ratio.
One measurement is a snapshot. Log your waist, hips and neck in 17 Fit: it works out your body fat by the same formula and keeps every measurement, so you see what changes. Progress photos stay on your phone.
Your body fat
29.4 %
Average range
- Fat mass
- 19.1 kg
- Lean mass
- 45.9 kg
- Waist‑to‑height ratio
- 0.45 · healthy
Enter a height of 120 to 230 cm, a neck of 20 to 70 cm, a waist of 40 to 200 cm and hips of 50 to 200 cm, with the waist larger than the neck. The weight, 35 to 250 kg, is optional.
With these measurements the formula gives under 2 % or over 70 % body fat, which can’t be right: check them.
An estimate: the tape method is usually within 3–4 percentage points of a lab scan.
Body fat 29.4 %: average range.
How to measure
Use a flexible tape, in the morning, standing relaxed, after a normal breath out. Keep it snug on the skin without pressing in; measure twice and take the average.
- Neck Just below the Adam’s apple, with the tape sloping slightly down to the front.
- Waist Men: around the navel. Women: at the narrowest point, usually above the navel.
- Hips Women only: around the widest part of the buttocks, with your feet together.
- Height Without shoes, standing straight against a wall.
Body fat ranges
The American Council on Exercise’s ranges for adults, in % body fat.
| Range | Women | Men |
|---|---|---|
| Essential fat | 10–13 | 2–5 |
| Athletes’ range | 14–20 | 6–13 |
| Fitness range | 21–24 | 14–17 |
| Average range | 25–31 | 18–24 |
| Above the average range | 32+ | 25+ |
Waist‑to‑height ratio
Your waist divided by your height. NICE, the UK’s health guidance body, advises keeping your waist to less than half your height. (NICE measures the waist halfway between the lowest rib and the top of the hip bone, so your figure here is close, not identical.)
| Ratio | Central fat (NICE) |
|---|---|
| under 0.5 | Healthy |
| 0.5–0.59 | Increased |
| 0.6 and over | High |
Body fat by waist
By the same formula, for a woman 165 cm tall (neck 33 cm, hips 100 cm) and a man 180 cm tall (neck 38 cm).
Women
| Waist, cm | Body fat, % |
|---|---|
| 60 | 21.7 |
| 65 | 24.3 |
| 70 | 26.9 |
| 75 | 29.4 |
| 80 | 31.9 |
| 85 | 34.3 |
| 90 | 36.6 |
| 95 | 38.9 |
Men
| Waist, cm | Body fat, % |
|---|---|
| 75 | 7.6 |
| 80 | 12.1 |
| 85 | 16.1 |
| 90 | 19.8 |
| 95 | 23.2 |
| 100 | 26.4 |
| 105 | 29.4 |
| 110 | 32.1 |
Questions and answers
How accurate is the US Navy method?
It’s an estimate: against a DEXA scan it’s usually within 3–4 percentage points, sometimes more. Measured the same way each time, the tape shows the direction of change well, which is why 17 Fit uses it for the trend.
What is a healthy body fat percentage?
The American Council on Exercise puts the average range at 25–31 % for women and 18–24 % for men, and the fitness range at 21–24 % for women and 14–17 % for men. Women need more essential fat than men.
Why does the formula need my neck?
Your neck stands in for the muscle and bone you carry: a thicker neck at the same waist means more lean mass. That’s how the method tells a big frame from a thick waist.
Why does my smart scale show a different number?
Smart scales send a weak current through your body and measure the resistance, which shifts with water, food and time of day. Neither number is a lab value; pick one method and compare it only with itself.
What does waist‑to‑height ratio tell me?
How much fat you carry around the middle, which BMI doesn’t show. NICE advises keeping your waist to less than half your height: a ratio under 0.5.
Can I lose fat from just one area?
Not by exercising that area: fat comes off the whole body, in an order set mostly by your genes. A calorie deficit with enough protein and strength training lowers it overall.
Who is the calculator not for?
Pregnant women, children and teenagers, and people who have had an amputation or have fluid retention: the formula wasn’t made for them. For a medical assessment, ask a doctor.
17 Fit
Measurements that show what the scale doesn’t
Log your tape measurements and weigh-ins in 17 Fit and see how your waist changes as the weight comes off, with your body fat by the same formula.
- Waist, hips, neck and more, with your body fat
- Weight trend and progress photos that stay on your phone
- Free food diary, no sign-up and no ads
