BMI
Body Mass Index (BMI)
BMI is weight divided by height squared; it describes weight relative to build but cannot tell muscle from fat.
Short answer
BMI is a quick weight-to-height ratio that cannot distinguish muscle from fat. On the result sheet it works as a companion to percent body fat, never as a verdict on its own.
What the value represents
BMI is weight in kilograms divided by the square of height in metres. It needs no body composition measurement at all — a scale and a tape measure are enough.
That simplicity is also its main weakness. BMI has no idea what your weight is made of. A muscular person can have a high BMI and very little fat, while someone with low muscle mass can sit inside the recommended range and still carry a high proportion of fat.
On an InBody result sheet BMI is therefore always shown next to Percent Body Fat. The pair is what carries meaning, not either figure alone.
- The ratio of weight to height, in kg/m².
- How large your weight is relative to your build — the manufacturer describes this as obesity by appearance.
- It does not represent the amount of fat, the amount of muscle, or how either is distributed.
How the value is produced
- A calculated value from two inputs: measured weight and the height entered before the measurement.
- The formula is BMI = weight (kg) ÷ height² (m²).
- If the entered height is wrong, BMI is wrong. The device does not measure height itself.
How to read the current value
- The manual gives the WHO range of 18.5–24.9 and the Asian range of 18.5–22.9. As the reference midpoint for calculating ideal weight it works with 22 for men and 21 for women in the Asian reference, and 22 and 21.5 in the Western one.
- That reference BMI is also what ideal weight is built from, and ideal weight in turn drives the Weight Control section of the result sheet.
- For children and adolescents up to 18 years, age-specific references apply, because the relationship between weight and height changes naturally during growth.
- BMI on its own does not support a conclusion. Always read Percent Body Fat from the same measurement alongside it.
How to read change over time
- BMI changes only with weight, since height stays the same. It therefore carries exactly the same short-term swings as weight: food, fluid and water retention.
- A change in BMI cannot tell you whether fat or muscle was lost. Fat mass and muscle mass are what answer that.
- A stable BMI with rising muscle and falling fat is a common and favourable situation that BMI alone does not capture at all.
General principles: how to read change between measurements →
What to read it with
- Percent Body Fat – separates a muscular build from a high fat share.
- Skeletal Muscle Mass – shows what the weight above the reference range is made of.
- Visceral Fat Area and waist circumference – add the distribution picture.
- Obesity Degree – expresses weight as a percentage of ideal weight.
Common misunderstandings
- A BMI above the range does not automatically mean excess fat. The manual explicitly describes a muscular type, where BMI is high and the fat share sits inside the range.
- A BMI inside the range does not automatically mean favourable body composition. The opposite case is called sarcopenic obesity: BMI looks ordinary while the fat share is high.
- BMI is not a measure of an individual health. It is a population tool that can be wrong in either direction for a given person.
- Different sources give different ranges. The Asian threshold is lower than the general WHO one.
What can affect the result short term
- The accuracy of the entered height — the one input that is not re-measured at every visit.
- Everything that moves weight: food, drink, clothing, time of day and water retention.
What to do next
- Treat BMI as an orientation point, not a conclusion. The decisive information sits in percent body fat and muscle mass.
- Check that your height is entered correctly in the system — a two-centimetre error shifts BMI noticeably.
- If what interests you is the risk tied to fat distribution, follow waist circumference and visceral fat instead of BMI.
What the value does not determine
- It does not distinguish muscle mass from fat mass.
- It says nothing about where fat is distributed in the body.
- It is not a diagnostic criterion for an individual.
- It depends entirely on the accuracy of the manually entered height.
On terminology
- The manufacturer distinguishes obesity by appearance (BMI) from actual obesity (percent body fat). These are two different views, not two measurements of the same thing.
In more depth, with sourcesIn more depth: why BMI stays in use despite its known limitsExpand the detailed explanation
BMI was created as a population indicator, and its strength lies in comparing large groups rather than individuals. The World Health Organization uses it to track the prevalence of overweight and obesity precisely because it needs only two easily obtained numbers and is comparable across countries.
For an individual, BMI fails systematically wherever body composition departs from the average: it overstates risk in people with high muscle mass and understates it in people with low muscle mass. The UK NICE guidance therefore recommends adding waist circumference as a measure of fat distribution in adults with a BMI below 35.
InBody uses BMI in two roles. The first is descriptive — obesity by appearance shown next to the actual fat share. The second is computational: the reference BMI establishes ideal weight, from which the recommended adjustment to weight, fat and muscle is derived.
Sources
- InBody 970 Result Sheet Interpretation (ENG_A_211104) — InBody Co., Ltd.
- Obesity and overweight — World Health Organization
- Obesity: identification, assessment and management (CG189) — National Institute for Health and Care Excellence
On this page
Commonly confused with
Related articles
Where to find it
The Muscle-Fat Analysis bar chart and the Obesity Analysis section that follows it.
- Reviewed by
- MojeInBody content team
- Date
An InBody measurement is not a diagnostic tool. Results do not determine health status and do not replace a medical examination.
FAQ
Frequently asked questions
Answers to what people ask most often about this value.
My BMI is high but my body fat is low. Is that a problem?
The manufacturer manual calls this combination a muscular type. A high BMI here reflects muscle mass rather than fat. What matters in such a case is the fat share and its distribution, not BMI itself.
Why is my BMI different on InBody than at my doctor?
BMI comes from weight and height. The difference arises from a different weight at a different time of day, or from a differently entered height. The calculation itself is the same everywhere.
Which BMI range applies to me?
The manual lists both the general WHO range of 18.5–24.9 and the lower Asian range of 18.5–22.9. Which one is relevant for you depends on context the device does not have, so treat the range as orientation only.
Explanations make the most sense alongside your own trend.
The public guide is open to everyone. The client portal adds your own value, history and the context of a specific measurement.