BMI (body mass index) is a simple calculation that compares body weight with height. It is commonly used as a screening measure for adults, but it is not a diagnosis and does not directly measure body fat, muscle mass or overall health. This guide explains the formula used by Tervilo, shows a worked example, and explains the limits you should understand before interpreting the result.
What BMI measures
BMI relates weight to the square of height. Because height appears twice in the formula, a change in height can have a meaningful effect on the result even when body weight stays the same.
BMI formula
Using metric units, the formula is:
BMI = weight in kilograms ÷ (height in metres × height in metres)For example, a person weighing 70 kg and measuring 1.75 m has a BMI of about 22.9.
Using pounds and inches
When you have weight in pounds and height in inches, the common imperial form is:
BMI = 703 × weight in pounds ÷ (height in inches × height in inches)The metric and imperial formulas produce the same BMI when the units are used correctly.
How to use Tervilo's BMI Calculator
- Open the Tervilo BMI Calculator.
- Choose the unit system you want to use.
- Enter your height and weight carefully.
- Calculate the result.
- Review the BMI value together with the category and limitation notes.
Adult BMI categories
For many adult screening contexts, BMI is commonly grouped into categories such as underweight, healthy weight, overweight and obesity. The exact interpretation can depend on the population and the guideline being used, so a calculator should not be treated as a universal clinical verdict.
Why BMI is only a screening measure
BMI does not distinguish muscle from fat and does not show where fat is distributed. A muscular person can have a higher BMI without having the same body-fat profile as another person at the same BMI. Age, sex, body composition and other health factors also matter.
BMI is not the same as body-fat percentage
BMI uses height and weight only. Body-fat percentage attempts to estimate the proportion of mass that is fat. Tervilo's Body Fat Calculator uses a different estimation approach. Neither number should be treated as a diagnosis.
Worked example with imperial units
A person who weighs 154 lb and is 68.9 inches tall has a BMI of about 22.8 using the imperial formula. The small difference from a metric example can come from rounding and the original measurements.
Why measurement accuracy matters
Small errors in height or weight can change the calculated value. Use a consistent measurement approach and the correct unit. Do not mix pounds with metres or kilograms with inches.
When BMI is not enough
A BMI value cannot, by itself, tell you whether a person is healthy, how much body fat they have, or what a healthy weight should be for an individual. For questions about your health, symptoms or treatment, use qualified clinical guidance rather than relying on a calculator alone.
How BMI categories are used
For adults, BMI is commonly grouped into screening categories using established cut points. These categories help organize population-level information, but the category alone does not describe a person's complete health profile. Body composition, waist circumference, medical history and other factors can change the practical interpretation.
BMI and children or teenagers
Adult BMI cutoffs should not simply be applied to children and adolescents. For younger people, BMI is interpreted using age- and sex-specific growth references. This is an important boundary for a general adult BMI calculator and a reason not to treat one adult reference table as universal for every age group.
What BMI cannot tell you
BMI does not measure where body fat is stored, how much muscle a person has, or how an individual feels or functions. A number can be mathematically correct and still be incomplete as a description of health. This is why BMI is more useful as one screening measure than as a standalone diagnosis.
How to use BMI alongside other information
For a general educational check, BMI can be considered together with other measurements and health context. If the number is unexpected, changing rapidly, or causing concern, a clinician can interpret it alongside the rest of the person's history and measurements.
Quick checklist
- □ I used matching units.
- □ I entered height and weight accurately.
- □ I understand BMI is a screening measure.
- □ I did not treat the result as a diagnosis.
- □ I considered body composition and other context.
Quick answer
BMI is calculated from weight and height: kilograms divided by metres squared, or 703 times pounds divided by inches squared. It is useful as a screening measure but does not measure body fat or diagnose health conditions.