Measuring Body Composition at Home: Waist-to-Hip Ratio and Body Fat
Two tape-measure numbers say more about health risk than a scale does: the waist-to-hip ratio, which describes where you carry fat, and an estimated body fat percentage, which describes how much of you is fat. Neither needs a clinic. Both depend heavily on measuring in the right place.
Where to put the tape
- Waist. Around the narrowest point between the bottom rib and the top of the hip bone — for most people just above the navel. Stand relaxed, breathe out normally, and don't pull the tape tight or suck in.
- Hip. Around the widest part of the buttocks.
- Neck (for the body-fat formula). Just below the larynx, with the tape sloping slightly down at the front.
- Keep the tape horizontal all the way round. Measure each site twice and average. A 1 cm error changes a body-fat estimate by 1–2 percentage points.
Waist-to-hip ratio
WHR = waist ÷ hip
An 80 cm waist and 100 cm hips give 0.80. Units cancel, so inches work too. The WHO risk bands:
| Lower risk | Higher risk | |
|---|---|---|
| Men | 0.95 or below | Above 1.0 |
| Women | 0.80 or below | Above 0.85 |
A higher ratio means proportionally more fat around the abdomen. Abdominal (visceral) fat sits around the organs and is more strongly tied to cardiovascular and metabolic risk than fat on the hips and thighs — which is why an "apple" shape and a "pear" shape at the same weight don't carry the same risk. The waist-to-hip ratio calculator applies these bands as you type.
Estimated body fat: the US Navy method
The US Navy (Hodgdon–Beckett) equations use the log of the waist-minus-neck circumference, scaled by height, because that difference tracks fat well across a population. The women's equation adds hip circumference to account for different fat distribution. The output goes through the Siri equation to become a percentage. It needs no calipers or scan — just the tape — and for an average build it lands within about 3 percentage points of a DEXA scan.
Rough categories (American Council on Exercise):
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Fitness | 14–17% | 21–24% |
| Acceptable | 18–24% | 25–31% |
| Above range | 25%+ | 32%+ |
The body fat calculator runs both equations.
Where these numbers break down
- Very lean or very muscular people. The formulas were fitted to a typical population; an athlete's waist-to-neck relationship falls outside it, so both WHR risk bands and the body-fat estimate become unreliable.
- Bone structure. A naturally narrow or broad frame shifts WHR without any change in fat.
- Bloating and fluid retention. A single reading taken on a bad day — a large meal, the premenstrual phase, a salty week — can be off by centimetres. Track a weekly average, measured at the same time of day.
- Pregnancy. Abdominal measurements aren't meaningful.
How this fits with BMI
BMI is the fastest screen — height and weight only — but it can't tell muscle from fat or say where fat sits. WHR adds the distribution; body fat percentage adds the amount. Read together they give a fuller picture than any one alone. None of them is a diagnosis; energy, fitness, blood pressure, and blood work matter more than any body-size number. See the BMI guide for more on that.
To turn a body-composition goal into an eating target, the calorie calculator estimates maintenance energy from height, weight, age, sex, and activity.