Relative Fat Mass
Divide height by waist, multiply by 20 and subtract from a constant: 64 for men, 76 for women. It needs one measurement fewer than the navy method, which also asks for the neck.
Your numbers
Body fat
24%
Waist-height ratio
0.5
Formula
Body fat = 64 (♂) / 76 (♀) − 20 × (Height (cm) ÷ Waist (cm))
It is an estimate, not a measurement. Take the waist at navel height after breathing out — moving the tape moves the answer a long way.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Sex (M1 / F0)Where the formula splits by sex — enter 1 for male, 0 for female. | 1 | 0 ~ 1 |
| Height (cm) (cm)Height in centimetres; converted to metres inside the formula. | 170 | 0 and up |
| Waist (cm) (cm)Waist at navel height, measured after breathing out. | 85 | 0 and up |
Step by step
Quick reference table
Results when only Height (cm) (cm) changes and everything else stays put.
| Height (cm) (cm) | Body fat (%) | Waist-height ratio |
|---|---|---|
| 85 | 44 | 1 |
| 128 | 33.9 | 0.664 |
| 170 | 24 | 0.5 |
| 255 | 4 | 0.333 |
| 340 | 0 | 0.25 |
What each result means
| Result | At default values |
|---|---|
| Body fat (%)The share of body weight that is fat. | 24 |
| Waist-height ratioWaist over height; the line people watch is 0.5. | 0.5 |
Common mistakes
It is an estimate, not a measurement. Take the waist at navel height after breathing out — moving the tape moves the answer a long way.
Glossary
- Sex (M1 / F0)
- Where the formula splits by sex — enter 1 for male, 0 for female.
- Height (cm)
- Height in centimetres; converted to metres inside the formula.
- Waist (cm)
- Waist at navel height, measured after breathing out.
- Body fat
- The share of body weight that is fat.
- Waist-height ratio
- Waist over height; the line people watch is 0.5.
Frequently asked questions
Q. How is Relative Fat Mass calculated?
Body fat = 64 (♂) / 76 (♀) − 20 × (Height (cm) ÷ Waist (cm)) — Divide height by waist, multiply by 20 and subtract from a constant: 64 for men, 76 for women. It needs one measurement fewer than the navy method, which also asks for the neck.
Q. Can you walk through an example?
With Sex (M1 / F0) 1, Height (cm) 170cm, Waist (cm) 85cm, the answer is Body fat 24%.
Q. What do I need to enter?
Enter Sex (M1 / F0), Height (cm), Waist (cm). The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only Height (cm) (cm) moves the answer to Height (cm) (cm) 85 → Body fat (%) 44 and Height (cm) (cm) 340 → Body fat (%) 0. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
It is an estimate, not a measurement. Take the waist at navel height after breathing out — moving the tape moves the answer a long way.
Related calculators
These calculators help you understand health figures; they do not replace diagnosis or prescription. See a clinician if you have symptoms.