BMI vs. Body Fat Percentage: What Each Number Can Tell You
Written by the Calculator Heaven team ·
BMI and body fat percentage are often mentioned in the same breath, but they measure different things. BMI is weight relative to height. Body fat percentage is the share of your weight that is fat. Two people with the same BMI can have very different amounts of body fat.
BMI in one paragraph
Body mass index is weight in kilograms divided by height in meters squared. Someone 5 ft 9 in tall weighing 160 lb has a BMI of 23.6. For adults, 18.5 to 24.9 is classed as a healthy weight, 25 to 29.9 as overweight, and 30 or more as obesity. Work out yours with the BMI calculator.
Its strength is simplicity. All you need is a scale and a tape measure, and across large populations it predicts health risk reasonably well. Its weakness is that it cannot see what the weight is made of.
Body fat percentage in one paragraph
Body fat percentage divides your fat mass by your total weight. The body fat calculator estimates it from neck, waist and (for women) hip measurements using the US Navy method, typically landing within three or four percentage points of a lab test.
| Category (American Council on Exercise) | Women | Men |
|---|---|---|
| Essential fat | 10-13% | 2-5% |
| Athletes | 14-20% | 6-13% |
| Fitness | 21-24% | 14-17% |
| Average | 25-31% | 18-24% |
| Obese | 32% and above | 25% and above |
Where the two disagree
- Muscular builds: a rugby player or weightlifter can have a BMI over 27 and body fat under 15%. BMI calls that overweight; body fat percentage does not.
- Lost muscle: an older adult can sit comfortably at a BMI of 23 while carrying a high proportion of fat. This is sometimes called normal-weight obesity, and BMI misses it entirely.
- Where the fat is: fat around the abdomen carries more health risk than fat on the hips and thighs. The Navy method includes the waist, so it picks up some of this. BMI picks up none.
Which one should you track?
For a quick check on whether your weight is in a reasonable range, BMI is enough for most people. If you lift weights, are over 60, or are changing your body composition through training, body fat percentage tells you more, because the scale can stay still while fat goes down and muscle goes up.
Whichever you choose, measure the same way each time: same tape, same time of day, same spots. The trend over months matters far more than any single reading.
Turning the number into a plan
Neither figure tells you what to eat. For that, start with your energy needs. The BMR calculator estimates what your body burns at rest, and the calorie calculator adds your activity level to give a daily target for maintaining, losing or gaining weight.
These tools are for general information. If either number worries you, or you have a medical condition, are pregnant, or have a history of disordered eating, talk to a doctor or registered dietitian before changing your diet.
Try the Body Fat CalculatorEstimate your body fat percentage with the US Navy tape-measure method, plus fat mass and lean mass.