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BMI vs Body Fat Percentage: What Each One Tells You

What BMI and body fat percentage each measure, how to work them out, and how to use both without being misled.

By Osama · Published October 13, 2026 · 8 min read

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Body mass index, or BMI, is the number most doctors, charts and calculators start with. It is quick and needs only a scale and a tape measure. But it is also one of the most criticised numbers in health, because it does not tell you what your weight is made of. Body fat percentage fills in part of that gap. This guide explains what each one measures, how they are calculated, and how to use them together.

The short version

  • BMI compares your weight with your height. It is a screening tool and cannot tell fat from muscle.
  • Body fat percentage estimates how much of your weight is fat. It is more informative, but home estimates are only approximate.
  • Two people with the same BMI can have very different amounts of body fat, and the reverse is also true.
  • Use both, and add your waist measurement and how you feel and perform. No single number gives the full picture.

What BMI is, and how it is calculated

BMI divides your weight by the square of your height. In metric units it is kilograms divided by metres squared. In US units you multiply the result by 703.

BMI = weight (lb) × 703 ÷ height (in)2Metric: BMI = weight (kg) ÷ height (m)2

For an example, take a man who is 70 inches tall (5 ft 10 in) and weighs 175 lb. His height squared is 4900, so BMI = 175 × 703 ÷ 4900 = 25.1. You can check any figure with our BMI Calculator.

Adult BMI categoriesAdult BMI categories: under 18.5 is underweight, 18.5 to 24.9 is a healthy weight, 25 to 29.9 is overweight and 30 or more is obesity. The example person has a BMI of 25.1.BMI (kg/m²)Example: 25.1Under15Healthy weight18.5Overweight25Obesity3040
The adult categories used by the NIH and the WHO. The example sits just above the 25 line, in the overweight range, even though he is not necessarily carrying excess fat.

The healthy range of 18.5 to 24.9 corresponds to a different weight at every height. The chart below shows the span for a range of heights.

Healthy weight range (BMI 18.5 to 24.9) by heightThe weight range that gives a BMI between 18.5 and 24.9 for adults of different heights, from about 95 lb at 5 ft 0 in to about 205 lb at 6 ft 4 in.0204060801001201401601802002205 ft 0 in95 to 1285 ft 4 in108 to 1455 ft 6 in115 to 1545 ft 8 in122 to 1645 ft 10 in129 to 1746 ft 0 in136 to 1846 ft 2 in144 to 1946 ft 4 in152 to 205
The weight range that gives a healthy-range BMI. At 5 ft 10 in it runs from about 129 lb to 174 lb, a wide band that accommodates different frames.
View the healthy weight ranges as numbers
HeightBMI 18.5BMI 24.9
5 ft 0 in95 lb128 lb
5 ft 4 in108 lb145 lb
5 ft 6 in115 lb154 lb
5 ft 8 in122 lb164 lb
5 ft 10 in129 lb174 lb
6 ft 0 in136 lb184 lb
6 ft 2 in144 lb194 lb
6 ft 4 in152 lb205 lb

What BMI cannot tell you

BMI is calculated from two numbers only, so it knows nothing about muscle, bone or where fat is stored. That leads to well-known blind spots:

  • Muscular people can be classed as overweight because muscle is dense, even when their body fat is low.
  • People who have lost muscle, such as some older adults, can have a healthy BMI while carrying a high proportion of fat.
  • Fat distribution matters. Fat around the waist is linked with higher health risk than the same amount carried on the hips and thighs.
  • Ancestry and age change the picture. Some health bodies suggest lower BMI cut-offs for people of Asian descent, for example.

For these reasons, BMI works best as a first screen for groups of people, and less well as a verdict on one individual.

What body fat percentage measures

Body fat percentage is the share of your total weight that is fat: fat mass divided by body weight. The rest is lean mass, which includes muscle, bone, organs and water. Some fat is essential for hormones, nerves and protecting organs, so zero is neither possible nor healthy.

Imagine two people who are both 5 ft 10 in and 175 lb. Both have a BMI of 25.1. One has 12% body fat and the other 28%.

Same height, same weight, different bodiesTwo hypothetical people are both 5 ft 10 in and 175 lb, so both have a BMI of 25.1. Person A has 12% body fat (21 lb of fat) and Person B has 28% (49 lb of fat).Fat mass (lb)Person A (12% fat)21 lbPerson B (28% fat)49 lbLean mass (lb)Person A (12% fat)154 lbPerson B (28% fat)126 lb
These two are hypothetical, chosen to make a point. The numbers show that the same BMI can sit on top of about 28 lb more fat and 28 lb less lean tissue.

Typical body fat ranges

There is no single official scale for healthy body fat, and the cut-offs differ between organisations. The ranges below are widely used in fitness settings (the American Council on Exercise publishes them). Women's ranges are higher partly because women carry more essential fat.

Body fat percentage ranges for menCommonly used body fat categories for men: essential fat 2 to 5 percent, athletes 6 to 13, fitness 14 to 17, average 18 to 24 and obese 25 percent and above.0%5%10%15%20%25%30%35%40%Essential fat2% to 5%Athletes6% to 13%Fitness14% to 17%Average18% to 24%Obese25% to 40%
Men: essential fat is the minimum the body needs to function normally. Ranges are rounded to whole percentages.
Body fat percentage ranges for womenCommonly used body fat categories for women: essential fat 10 to 13 percent, athletes 14 to 20, fitness 21 to 24, average 25 to 31 and obese 32 percent and above.0%5%10%15%20%25%30%35%40%45%Essential fat10% to 13%Athletes14% to 20%Fitness21% to 24%Average25% to 31%Obese32% to 45%
Women: the same categories shifted upward. These are descriptive bands and not a diagnosis.

How body fat is estimated at home

The most accurate methods (DEXA scans, underwater weighing and similar) need a clinic or lab. At home, the usual choice is the US Navy method, which estimates body fat from height, neck and waist (plus hips for women) using tape measurements. For men the metric version is:

Body fat % = 495 ÷ (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450Measurements in centimetres. Women use waist + hip − neck, with different constants.

Using the same man, with a 34 inch waist and 15 inch neck: waist − neck = 48.3 cm and height = 177.8 cm. The formula gives about 17.4% body fat, which is 31 lb of fat and 144 lb of lean mass. That is in the "fitness" band for men, even though his BMI says overweight. Our Body Fat Calculator uses this method.

How accurate is it? Tape measurements are sensitive to where you place the tape and how relaxed you are, and a one-centimetre error in the waist moves the result by a noticeable amount. Treat the answer as a rough estimate that can be several percentage points off, and use it to track change over time, measuring the same way each time.

Which should you use?

  • For a quick check, BMI is fine. If it is in the healthy range and your waist is within a healthy size, there is little more to learn.
  • If you lift weights or are very active, body fat percentage describes you better than BMI.
  • If BMI is high or low, check your waist. NIH guidance flags a waist above about 40 inches for men and 35 inches for women as a risk marker.
  • For health decisions, look at blood pressure, blood sugar, cholesterol, fitness and family history, and talk to a doctor. The numbers here are starting points.

Common questions

Is BMI accurate?

It is a reasonable screening tool for large groups, but it can misclassify individuals. It cannot tell muscle from fat, so very muscular people may be labelled overweight and people with little muscle may be labelled healthy.

What is a healthy body fat percentage?

It depends on age and sex. Commonly used fitness ranges put average men at about 18 to 24% and average women at about 25 to 31%, with lower numbers for athletes. Essential fat sets a floor of roughly 2 to 5% for men and 10 to 13% for women.

Is the Navy body fat formula reliable?

It is a convenient estimate and is often close for average builds, but it can be off by several percentage points. Use it to track trends, measuring in the same way each time, rather than as a precise figure.

Why is BMI different for athletes?

Muscle weighs more than the same volume of fat, so people with a lot of muscle can have a BMI above 25 with low body fat. For them, body fat percentage is the more useful number.

Does BMI work for children?

Not with adult cut-offs. For children and teenagers, BMI is compared with growth charts for the same age and sex, and a doctor interprets the result.

Sources and further reading

This guide is for general education and is not medical advice. BMI and body fat estimates are screening tools. Speak to a doctor or registered dietitian about your own health and weight.

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