BMI tells you how heavy you are for your height. Body fat percentage tells you what that weight is actually made of — and for most people chasing a fitness goal, that’s the number that matters. This guide shows you how to calculate body fat two ways at home, how to read the men’s and women’s charts, how to turn the result into fat mass and lean mass, and how accurate it all really is. For instant numbers, use our free Body Fat Calculator.

The Two At-Home Body Fat Formulas

You don’t need a lab to get a useful estimate. The two most popular at-home methods are the U.S. Navy tape method and the BMI (Deurenberg) method.

U.S. Navy method — uses tape-measure circumferences plus height (all in cm):

Men: BF% = 495 ÷ [1.0324 − 0.19077·log₁₀(waist − neck) + 0.15456·log₁₀(height)] − 450
Women: BF% = 495 ÷ [1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.22100·log₁₀(height)] − 450

BMI method — when you don’t have a tape, estimate from BMI, age and sex:

BF% = 1.20 × BMI + 0.23 × age − 10.8 × sex − 5.4  (sex = 1 for men, 0 for women)

Know your measurements and you can run either by hand — or skip the math and let the calculator do all of it.

Worked example — Navy method (man)

A man who is 178 cm tall with a 38 cm neck and an 84 cm waist: waist − neck = 46. Dropping that into the men’s formula gives roughly 15.7% body fat, which sits in the “fitness” range.

Worked example — Navy method (woman)

A woman who is 165 cm tall with a 31 cm neck, 68 cm waist and 93 cm hips: waist + hip − neck = 130. The women’s formula returns about 23.3% body fat — also in the “fitness” range, because women’s healthy ranges run higher than men’s.

Worked example — BMI method

A 30-year-old man, 178 cm and 78 kg, has a BMI of 24.6. The BMI method gives 1.20 × 24.6 + 0.23 × 30 − 10.8 − 5.4 ≈ 20.2% body fat. Notice it lands a few points higher than the tape result — that’s the normal gap between methods, which is why you should pick one and stick with it.

Body Fat Percentage Chart (Men & Women)

The American Council on Exercise (ACE) describes these general bands — and they’re the numbers worth memorising:

• Essential fat: men 2–5%, women 10–13%
• Athletes: men 6–13%, women 14–20%
• Fitness: men 14–17%, women 21–24%
• Average / acceptable: men 18–24%, women 25–31%
• Obese: men 25%+, women 32%+

Women naturally carry more essential fat than men for hormonal and reproductive reasons, so a “healthy” figure for a woman is several points higher than for a man at the same fitness level. Comparing a man’s number to a woman’s chart (or vice versa) is the most common mistake people make.

Fat Mass vs Lean Mass — What the Numbers Mean

Once you know your body fat percentage, two more useful numbers fall out of it:

Fat mass = weight × body fat %
Lean mass = weight − fat mass

For that 78 kg man at 20.2%, fat mass is about 15.8 kg and lean mass about 62.2 kg. Tracking lean mass over time is the real prize: it tells you whether a change in weight came from fat or from muscle — something the scale alone can never show you. Our Body Fat Calculator displays both automatically when you enter your weight.

How to Measure Yourself Correctly

The Navy method is only as good as your tape work — sloppy measurements are the number-one source of error. Use a flexible cloth or fibreglass tape, keep it snug but not digging in, and measure on bare skin first thing in the morning:

• Neck: just below the larynx (Adam’s apple), with the tape sloping slightly downward to the front.
• Waist (men): across the navel, standing relaxed — don’t suck in.
• Waist (women): at the narrowest point of the torso.
• Hips (women): around the widest part of the buttocks.

Take each measurement two or three times and use the average. Always re-measure under the same conditions so your trend line stays honest.

Body Fat % vs BMI — Which Should You Use?

BMI is fast and needs only a scale, but it can’t tell muscle from fat. A lifter and someone carrying excess fat can share an identical BMI while looking and performing completely differently. Body fat percentage looks past total weight to your composition, so it isn’t fooled by muscle — which is exactly why athletes and anyone doing a “recomp” prefer it. The trade-off: body fat is harder to measure precisely, so the estimate carries more uncertainty. Most people get the best picture by checking both. Compare yours with our BMI Calculator to see the difference for yourself.

How Accurate Are These Methods?

Treat any at-home number as a ballpark, not gospel. The Navy and BMI methods typically land within about 3–4 percentage points of a lab measurement, and both lose accuracy at the extremes — very lean or very muscular bodies, and the very overweight. The gold standards are a DEXA scan or hydrostatic (underwater) weighing, with calipers and bioelectrical scales somewhere in between. The good news: even an imperfect method is excellent at tracking change, as long as you measure the same way every time.

Improving Your Body Composition

If you want to shift the ratio of fat to muscle, the fundamentals beat any gadget or hack:

• Strength train. Building or keeping muscle is what lowers body fat percentage even when the scale barely moves.
• Prioritise protein and whole foods. Adequate protein supports muscle; plan it with our Macro Calculator.
• Know your energy needs. Our TDEE and Calorie calculators show your daily burn so changes are gradual, not extreme.
• Sleep and stay consistent. Recovery and steady habits move the needle far more than crash efforts.
• Track the trend, not the day. Re-measure every few weeks and watch the direction over time.

And if a number ever starts to feel like a source of stress rather than a useful signal, that’s the moment to talk to a doctor or registered dietitian rather than push harder alone.