Body fat calculator
Your body fat percentage from a tape measure.
Output
Enter your height, waist and neck.
Your files stay on your device
This tool runs entirely in your browser. What you paste is processed on your device and is never sent to a server, so it is safe to use with tokens, keys and unpublished text.
Example
Example: 5′5″ and 150 lb, measured in inches and checked again eight weeks later
A woman 5'5" tall and 150 lb measures with a soft tape: waist 31 in at its narrowest, neck 13.5 in just below the larynx, hips 40 in at their widest. Method: Tape measure (Navy method), Woman, US / imperial; the height can be typed 5'5", 5 ft 5 or 65.
- Result: 31.4% body fat, Average (25–31.9%), 47.1 lb of fat mass and 102.9 lb of lean mass.
- Eight weeks later: 146 lb, waist 30 in, hips 39.5 in, neck the same. Now 29.5%, still Average, with 43.1 lb of fat and the same 102.9 lb of lean mass: on these figures, the 4 lb lost was fat.
- The same first day with From BMI and age (age 42): BMI 25.0 gives 34.2%, Obese (32% and over) — nearly three points above the tape, which is why the BMI method is the rougher one.
- Weight in stone? Type it as the scale shows it: 10 st 10 lb, or 10st 10, is read as 10 × 14 + 10 = 150 lb.
| Day | Waist | Hips | Weight | Body fat | Fat mass | Lean mass |
|---|---|---|---|---|---|---|
| Week 0, tape | 31 in | 40 in | 150 lb | 31.4%, Average | 47.1 lb | 102.9 lb |
| Week 8, tape | 30 in | 39.5 in | 146 lb | 29.5%, Average | 43.1 lb | 102.9 lb |
| Week 0, BMI and age 42 | — | — | 150 lb | 34.2%, Obese | 51.3 lb | 98.7 lb |
Compare like with like: the same tape, the same spots, the same time of day. A drop of about two points over eight weeks is the kind of trend the tape shows well; the number itself is an estimate, not a diagnosis — ask your doctor what is healthy for you.
How it works
- Measure with a soft tape, snug but not pressing: neck just below the Adam’s apple; waist level with the navel (men) or at its narrowest (women); women also the hips at their widest.
- Choose man or woman and your units, then enter height, weight and the measurements.
- Read your body fat percentage, its category, and your fat and lean mass.
Frequently asked questions
- How accurate is the Navy method?
- It is a formula from tape measurements (Hodgdon and Beckett, 1984) and is usually within a few percentage points of lab methods — good for following your own trend with the same tape and the same spots.
- What do the categories mean?
- They are the American Council on Exercise ranges. For men: essential fat 2–5 %, athletes 6–13 %, fitness 14–17 %, average 18–24 %, obese 25 % and over; for women: 10–13, 14–20, 21–24, 25–31 and 32 % and over.
- Can I enter my weight in stone?
- Yes: type it as the scale shows it, “10 st 10 lb”, “10st 10” or “12 st”. A stone is 14 lb, so 10 st 10 lb is read as 150 lb and 12 st as 168 lb. Pounds, or kilograms with the unit (“68 kg”), work too, whichever units are chosen.
- When should I use the BMI method?
- When you have no tape measure. It is rougher — it can’t tell muscle from fat, so it overestimates muscular people — and it is for adults only.
- How do I type my height in feet and inches?
- With US / imperial, any of 5'5", 5′5″, 5 ft 5, 5ft 5in or 5 5; a plain number is inches, so 65 is the same height. With metric, 165, 165 cm and 1.65 m all mean 165 cm. Waist, neck and hips take inches or centimetres the same way.
- Is anything saved?
- No. It is worked out in your browser. It is an estimate, not a medical diagnosis.